diff --git a/src/core/Axios.ts b/src/core/Axios.ts
index c76c733..4c17da2 100644
--- a/src/core/Axios.ts
+++ b/src/core/Axios.ts
@@ -53,6 +53,7 @@ export interface AxiosRequestConfig {
   cancelToken?: CancelToken;
   data?: AxiosRequestData | AxiosRequestFormData | AxiosRequestFormData;
   dataType?: 'json' | '其他';
+  download?: boolean;
   enableHttp2?: boolean;
   enableQuic?: boolean;
   enableCache?: boolean;
@@ -68,6 +69,7 @@ export interface AxiosRequestConfig {
   transformRequest?: AxiosTransformer | AxiosTransformer[];
   transformResponse?: AxiosTransformer | AxiosTransformer[];
   timeout?: number;
+  upload?: boolean;
   url?: string;
   validateStatus?: (status: number) => boolean;
 }
diff --git a/src/core/adapter.ts b/src/core/adapter.ts
index 77551b8..c64c722 100644
--- a/src/core/adapter.ts
+++ b/src/core/adapter.ts
@@ -2,6 +2,7 @@ import {
   isEmptyArray,
   isFunction,
   isPlainObject,
+  isString,
   isUndefined,
 } from '../helpers/is';
 import { assert, throwError } from '../helpers/utils';
@@ -15,6 +16,8 @@ import {
   AxiosResponseError,
 } from './Axios';
 
+export type AdapterRequestType = 'request' | 'download' | 'upload';
+
 export type AdapterRequestMethod =
   | 'OPTIONS'
   | 'GET'
@@ -25,8 +28,6 @@ export type AdapterRequestMethod =
   | 'TRACE'
   | 'CONNECT';
 
-export type AdapterRequestType = 'request' | 'download' | 'upload';
-
 export interface AxiosAdapterRequestConfig extends AxiosRequestConfig {
   type: AdapterRequestType;
   method: AdapterRequestMethod;
@@ -187,6 +188,16 @@ export function createAdapter(platform: AxiosPlatform): AxiosAdapter {
     upload: AxiosAdapterUpload,
     config: AxiosAdapterRequestConfig,
   ): AxiosAdapterTask | void {
+    assert(isPlainObject(config.data), '上传文件时 data 需要是一个 object');
+    assert(
+      isString(config.data!.fileName),
+      '上传文件时 data.fileName 需要是一个 string',
+    );
+    assert(
+      isString(config.data!.filePath),
+      '上传文件时 data.filePath 需要是一个 string',
+    );
+
     const {
       fileName,
       filePath,
diff --git a/src/core/flattenHeaders.ts b/src/core/flattenHeaders.ts
index 71db3c1..982c3b5 100644
--- a/src/core/flattenHeaders.ts
+++ b/src/core/flattenHeaders.ts
@@ -1,5 +1,5 @@
 import { isPlainObject } from '../helpers/is';
-import { omit } from '../helpers/utils';
+import { omit, toLowerCase } from '../helpers/utils';
 import {
   AxiosRequestConfig,
   AxiosRequestMethodAlias,
@@ -10,11 +10,11 @@ export function flattenHeaders(
   config: AxiosRequestConfig,
 ): AxiosRequestHeaders | undefined {
   if (!isPlainObject(config.headers)) {
-    return;
+    return config.headers;
   }
 
   const common = 'common';
-  const method = config.method?.toLowerCase() ?? 'get';
+  const method = toLowerCase<AxiosRequestMethodAlias>(config.method, 'get');
   const alias: AxiosRequestMethodAlias[] = [
     'options',
     'get',
diff --git a/src/core/generateType.ts b/src/core/generateType.ts
index dbdb642..f807df8 100644
--- a/src/core/generateType.ts
+++ b/src/core/generateType.ts
@@ -1,37 +1,17 @@
-import { isPlainObject, isString } from 'src/helpers/is';
-import { assert } from '../helpers/utils';
+import { toLowerCase } from '../helpers/utils';
 import { AdapterRequestType } from './adapter';
-import { AxiosRequestConfig } from './Axios';
+import { AxiosRequestConfig, AxiosRequestMethodAlias } from './Axios';
 
 export function generateType(config: AxiosRequestConfig): AdapterRequestType {
   let requestType: AdapterRequestType = 'request';
 
-  if (
-    !isPlainObject(config.headers) ||
-    !/multipart\/form-data/.test(
-      config.headers['Content-Type'] ?? config.headers['content-type'] ?? '',
-    )
-  ) {
-    return requestType;
-  }
-
-  const method = config.method?.toLowerCase() ?? 'get';
-
-  if (method === 'post') {
-    assert(isPlainObject(config.data), '上传文件时 data 需要是一个 object');
-    assert(
-      isString(config.data!.fileName),
-      '上传文件时 data.fileName 需要是一个 string',
-    );
-    assert(
-      isString(config.data!.filePath),
-      '上传文件时 data.filePath 需要是一个 string',
-    );
+  const method = toLowerCase<AxiosRequestMethodAlias>(config.method, 'get');
 
+  if (config.upload && method === 'post') {
     requestType = 'upload';
   }
 
-  if (method === 'get') {
+  if (config.download && method === 'get') {
     requestType = 'download';
   }
 
diff --git a/src/core/request.ts b/src/core/request.ts
index 27f1095..cb78902 100644
--- a/src/core/request.ts
+++ b/src/core/request.ts
@@ -1,5 +1,5 @@
 import { isFunction, isPlainObject } from '../helpers/is';
-import { assert } from '../helpers/utils';
+import { assert, toUpperCase } from '../helpers/utils';
 import {
   AxiosAdapterRequestConfig,
   AdapterRequestMethod,
@@ -41,7 +41,7 @@ export function request<TData = any>(
       ...config,
       url: config.url ?? '',
       type: generateType(config),
-      method: (config.method?.toUpperCase() as AdapterRequestMethod) ?? 'GET',
+      method: toUpperCase<AdapterRequestMethod>(config.method, 'GET'),
       success,
       fail,
     };
diff --git a/src/helpers/utils.ts b/src/helpers/utils.ts
index 6854f1c..47b6320 100644
--- a/src/helpers/utils.ts
+++ b/src/helpers/utils.ts
@@ -1,4 +1,4 @@
-import { isPlainObject } from './is';
+import { isPlainObject, isString } from './is';
 
 export function deepMerge<T = any>(...objs: T[]): T {
   const result: AnyObject = {};
@@ -52,3 +52,19 @@ export function assert(condition: boolean, msg: string) {
 export function throwError(msg: string): void {
   throw new Error(`[axios-miniprogram]:${msg}`);
 }
+
+export function toLowerCase<T extends string>(value: any, defaultValue: T): T {
+  if (!isString(value)) {
+    return defaultValue;
+  }
+
+  return value.toLowerCase() as T;
+}
+
+export function toUpperCase<T extends string>(value: any, defaultValue: T): T {
+  if (!isString(value)) {
+    return defaultValue;
+  }
+
+  return value.toUpperCase() as T;
+}