几点意见：
1.您的示例是AFNetworking 1.x。AFNetworking 3.x副本可能如下所示：

NSURL *fileURL = [[NSBundle mainBundle] URLForResource:@"1" withExtension:@"png"];

// If you need to build dictionary dynamically as in your question, that's fine,
// but sometimes array literals are more concise way if the structure of
// the dictionary is always the same.

// Also note that these keys do _not_ match what are present in the `curl`
// so please double check these keys (e.g. `discountDiscription` vs
// `discountDescription` vs `name`)!

NSDictionary *offerDTO = @{@"code"                : @"",
                           @"discountDescription" : @"Testing",
                           @"remark"              : @"Test",
                           @"validityDate"        : @"07-05-2015",
                           @"creatorCode"         : @"C-7",
                           @"merchantCode"        : @"M-1",
                           @"isApproved"          : @YES,
                           @"discountValue"       : @2.4,
                           @"discountType"        : @"FREE"};

// `AFHTTPSessionManager` is AFNetworking 3.x equivalent to `AFHTTPClient` in AFNetworking 1.x

NSURL *baseURL = [NSURL URLWithString:@"http://serverurl:8180"];
AFHTTPSessionManager *manager = [[AFHTTPSessionManager alloc] initWithBaseURL:baseURL];

// The `POST` method both creates and issues the request

[manager POST:@"/restapi/offer/add" parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData>  _Nonnull formData) {
    NSError *error;
    BOOL success;

    success = [formData appendPartWithFileURL:fileURL
                                         name:@"image"
                                     fileName:@"image.jpg"
                                     mimeType:@"image/png"
                                        error:&error];
    NSAssert(success, @"Failure adding file: %@", error);

    success = [formData appendPartWithFileURL:fileURL
                                         name:@"letterhead"
                                     fileName:@"image.jpg"
                                     mimeType:@"image/png"
                                        error:&error];
    NSAssert(success, @"Failure adding file: %@", error);

    NSData *jsonData = [NSJSONSerialization dataWithJSONObject:offerDTO options:0 error:&error];
    NSAssert(jsonData, @"Failure building JSON: %@", error);

    // You could just do:
    //
    // [formData appendPartWithFormData:jsonData name:@"offerDTO"];
    //
    // but I now notice that in your `curl`, you set the `Content-Type` for the
    // part, so if you want to do that, you could do it like so:

    NSDictionary *jsonHeaders = @{@"Content-Disposition" : @"form-data; name=\"offerDTO\"",
                                  @"Content-Type"        : @"application/json"};
    [formData appendPartWithHeaders:jsonHeaders body:jsonData];
} progress:^(NSProgress * _Nonnull uploadProgress) {
    // do whatever you want here
} success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
    NSLog(@"responseObject = %@", responseObject);
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
    NSLog(@"error = %@", error);
}];

1.你在这里创建了一个操作，但是从来没有把它添加到队列中来启动它。我假设你在其他地方也这样做。值得注意的是AFHTTPSessionManager不支持像已经过时的AFHTTPRequestOperationManager或AFHTTPClient那样的操作。上面的代码只是自动启动操作。
1.注意，AFNetworking现在假设响应是JSON，假设代码建议响应是JSON，那么注意不需要JSONObjectWithData，因为已经为您完成了。

• 现在您的代码是（a）创建UIImage;（B）将其转换回NSData;以及（c）将其添加到formData。由于许多原因，这是低效的：
• 具体来说，通过获取图像资源，将其加载到UIImage中，然后使用UIImageJPEGRepresentation，可能会使生成的NSData比原始资源大得多。您可能会考虑直接获取原始资源，完全绕过UIImage，然后发送它（显然，如果要发送PNG，也要更改MIME类型）。
• 将NSData添加到请求的过程可能会导致内存占用量增加。通常，如果您提供一个文件名，它可以将内存使用峰值保持在较低的水平。

您可以将NSDictionary直接传递到参数字段中的管理器发布块

UIImage *imageToPost = [UIImage imageNamed:@"1.png"];
NSData *imageData = UIImageJPEGRepresentation(imageToPost, 1.0);

NSDictionary *offerDTO = @{@"code"                : @"",
                           @"discountDescription" : @"Testing",
                           @"remark"              : @"Test",
                           @"validityDate"        : @"07-05-2015",
                           @"creatorCode"         : @"C-7",
                           @"merchantCode"        : @"M-1",
                           @"isApproved"          : @YES,
                           @"discountValue"       : @2.4,
                           @"discountType"        : @"FREE"};

NSURL *baseURL = [NSURL URLWithString:@"http://serverurl:8180"];
AFHTTPRequestOperationManager *manager = [[AFHTTPRequestOperationManager alloc] initWithBaseURL:baseURL];

[manager POST:@"/restapi/offer/add" parameters:offerDTO constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
    [formData appendPartWithFileData:imageData name:@"image"
                            fileName:@"image.jpg"
                            mimeType:@"image/jpeg"];

    [formData appendPartWithFileData:imageData name:@"letterhead"
                            fileName:@"image.jpg"
                            mimeType:@"image/jpeg"];

    [formData appendPartWithHeaders:jsonHeaders body:jsonData];
} success:^(AFHTTPRequestOperation *operation, id responseObject) {
    NSLog(@"responseObject = %@", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    NSLog(@"error = %@", error);
}]

;