diff --git a/HISTORY.md b/HISTORY.md
index ec95c29f..4cd557f7 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -1,5 +1,14 @@
 # Release History
 
+## 2.1.1 (2019-04-11)
+
+**Features**
+
+refactor upload files mechanism with [requests-toolbelt](https://toolbelt.readthedocs.io/en/latest/user.html#multipart-form-data-encoder):
+
+- simplify usage syntax, detect mimetype with [filetype](https://github.com/h2non/filetype.py).
+- support upload multiple fields.
+
 ## 2.1.0 (2019-04-10)
 
 **Features**
diff --git a/Pipfile b/Pipfile
index 83a9df29..5e4c9ad5 100644
--- a/Pipfile
+++ b/Pipfile
@@ -11,6 +11,7 @@ har2case = "*"
 colorama = "*"
 colorlog = "*"
 requests-toolbelt = "*"
+filetype = "*"
 
 [dev-packages]
 Flask = "<1.0.0"
diff --git a/httprunner/__about__.py b/httprunner/__about__.py
index 01d4dc4f..cc08e19b 100644
--- a/httprunner/__about__.py
+++ b/httprunner/__about__.py
@@ -1,7 +1,7 @@
 __title__ = 'HttpRunner'
 __description__ = 'One-stop solution for HTTP(S) testing.'
 __url__ = 'https://github.com/HttpRunner/HttpRunner'
-__version__ = '2.1.0'
+__version__ = '2.1.1'
 __author__ = 'debugtalk'
 __author_email__ = 'mail@debugtalk.com'
 __license__ = 'Apache-2.0'
diff --git a/httprunner/built_in.py b/httprunner/built_in.py
index e3e0d1bd..7f26e8ea 100644
--- a/httprunner/built_in.py
+++ b/httprunner/built_in.py
@@ -12,13 +12,18 @@ import re
 import string
 import time
 
+import filetype
 from httprunner.compat import basestring, builtin_str, integer_types, str
 from httprunner.exceptions import ParamsError
 from requests_toolbelt import MultipartEncoder
 
+PWD = os.getcwd()
+
+
+###############################################################################
+##  built-in functions
+###############################################################################
 
-""" built-in functions
-"""
 def gen_random_string(str_len):
     """ generate random string with specified length
     """
@@ -38,24 +43,68 @@ def get_current_date(fmt="%Y-%m-%d"):
     """
     return datetime.datetime.now().strftime(fmt)
 
-def multipart_encoder(field_name, file_path, file_type=None, file_headers=None):
-    if not os.path.isabs(file_path):
-        file_path = os.path.join(os.getcwd(), file_path)
 
-    filename = os.path.basename(file_path)
-    with open(file_path, 'rb') as f:
-        fields = {
-            field_name: (filename, f.read(), file_type)
-        }
+###############################################################################
+##  upload files with requests-toolbelt
+#   e.g.
+#   - test:
+#      name: upload file
+#      variables:
+#          file_path: "data/test.env"
+#          multipart_encoder: ${multipart_encoder(file=$file_path)}
+#      request:
+#          url: /post
+#          method: POST
+#          headers:
+#              Content-Type: ${multipart_content_type($multipart_encoder)}
+#          data: $multipart_encoder
+#      validate:
+#          - eq: ["status_code", 200]
+#          - startswith: ["content.files.file", "UserName=test"]
+###############################################################################
+
+def multipart_encoder(**kwargs):
+    """ initialize MultipartEncoder with uploading fields.
+    """
+    def get_filetype(file_path):
+        file_type = filetype.guess(file_path)
+        if file_type:
+            return file_type.mime
+        else:
+            return "text/html"
+
+    fields_dict = {}
+    for key, value in kwargs.items():
+
+        if os.path.isabs(value):
+            _file_path = value
+            is_file = True
+        else:
+            global PWD
+            _file_path = os.path.join(PWD, value)
+            is_file = os.path.isfile(_file_path)
+
+        if is_file:
+            filename = os.path.basename(_file_path)
+            with open(_file_path, 'rb') as f:
+                mime_type = get_filetype(_file_path)
+                fields_dict[key] = (filename, f.read(), mime_type)
+        else:
+            fields_dict[key] = value
+
+    return MultipartEncoder(fields=fields_dict)
 
-    return MultipartEncoder(fields)
 
 def multipart_content_type(multipart_encoder):
+    """ prepare Content-Type for request headers
+    """
     return multipart_encoder.content_type
 
 
-""" built-in comparators
-"""
+###############################################################################
+##  built-in comparators
+###############################################################################
+
 def equals(check_value, expect_value):
     assert check_value == expect_value
 
diff --git a/httprunner/loader.py b/httprunner/loader.py
index ade04d6a..3fddb238 100644
--- a/httprunner/loader.py
+++ b/httprunner/loader.py
@@ -8,8 +8,7 @@ import os
 import sys
 
 import yaml
-from httprunner import exceptions, logger, parser, utils, validator
-
+from httprunner import built_in, exceptions, logger, parser, utils, validator
 
 ###############################################################################
 ##   file loader
@@ -263,7 +262,6 @@ def load_module_functions(module):
 def load_builtin_functions():
     """ load built_in module functions
     """
-    from httprunner import built_in
     return load_module_functions(built_in)
 
 
@@ -703,6 +701,7 @@ def load_project_tests(test_path, dot_env_path=None):
     # locate PWD and load debugtalk.py functions
 
     project_mapping["PWD"] = project_working_directory
+    built_in.PWD = project_working_directory
     project_mapping["functions"] = debugtalk_functions
 
     # load api
diff --git a/httprunner/runner.py b/httprunner/runner.py
index 5df077b5..d5f96a6d 100644
--- a/httprunner/runner.py
+++ b/httprunner/runner.py
@@ -267,7 +267,7 @@ class Runner(object):
         self.session_context.update_session_variables(extracted_variables_mapping)
 
         # validate
-        validators = test_dict.get("validate", [])
+        validators = test_dict.get("validate") or test_dict.get("validators") or []
         try:
             self.session_context.validate(validators, resp_obj)
         except (exceptions.ParamsError, exceptions.ValidationFailure, exceptions.ExtractFailure):
diff --git a/setup.py b/setup.py
index 3c8effee..9e118d2b 100644
--- a/setup.py
+++ b/setup.py
@@ -21,7 +21,8 @@ install_requires = [
     "har2case",
     "colorama",
     "colorlog",
-    "requests_toolbelt"
+    "requests_toolbelt",
+    "filetype"
 ]
 
 class UploadCommand(Command):
diff --git a/tests/httpbin/load_image.yml b/tests/httpbin/load_image.yml
index 1243ef86..4ea6da75 100644
--- a/tests/httpbin/load_image.yml
+++ b/tests/httpbin/load_image.yml
@@ -7,7 +7,7 @@
     request:
         url: /image/png
         method: GET
-    validators:
+    validate:
         - eq: ["status_code", 200]
 
 - test:
@@ -15,7 +15,7 @@
     request:
         url: /image/jpeg
         method: GET
-    validators:
+    validate:
         - eq: ["status_code", 200]
 
 - test:
@@ -23,7 +23,7 @@
     request:
         url: /image/webp
         method: GET
-    validators:
+    validate:
         - eq: ["status_code", 200]
 
 - test:
@@ -31,6 +31,6 @@
     request:
         url: /image/svg
         method: GET
-    validators:
+    validate:
         - eq: ["status_code", 200]
 
diff --git a/tests/httpbin/upload.yml b/tests/httpbin/upload.yml
index 3abd8c76..344b90bd 100644
--- a/tests/httpbin/upload.yml
+++ b/tests/httpbin/upload.yml
@@ -5,17 +5,15 @@
 - test:
     name: upload file
     variables:
-        field_name: "file"
-        file_path: "LICENSE"
-        file_type: "text/html"
-        multipart_encoder: ${multipart_encoder($field_name, $file_path, $file_type)}
+        file_path: "data/test.env"
+        multipart_encoder: ${multipart_encoder(file=$file_path)}
     request:
         url: /post
         method: POST
         headers:
             Content-Type: ${multipart_content_type($multipart_encoder)}
         data: $multipart_encoder
-    validators:
+    validate:
         - eq: ["status_code", 200]
-        - startswith: ["content.files.file", "MIT License"]
+        - startswith: ["content.files.file", "UserName=test"]