那么你的模拟器很可能运行的是iOS 9。在iOS 9中，TLS 1.2是强制执行的。如果你不使用它，你的请求将失败。
请查看this post以了解更多信息。
您可以将以下代码放在Info.plist中绕过它：

<key>NSAppTransportSecurity</key>
<dict>
  <!--Include to allow all connections (DANGER)-->
  <key>NSAllowsArbitraryLoads</key>
      <true/>
</dict>

但它只是一个临时解决办法，直到您可以实现TLS1.2。

你没有绕过TLS层。请找到下面的答案，它对我使用自签名证书有效。
以下是与自签名SSL证书配合使用的代码更改

func URLSession(session: NSURLSession, didReceiveChallenge challenge: NSURLAuthenticationChallenge, completionHandler: (NSURLSessionAuthChallengeDisposition, NSURLCredential?) -> Void) {

    if challenge.protectionSpace.authenticationMethod == (NSURLAuthenticationMethodServerTrust) {

    let serverTrust:SecTrustRef = challenge.protectionSpace.serverTrust!
    let certificate: SecCertificateRef = SecTrustGetCertificateAtIndex(serverTrust, 0)!
    let remoteCertificateData = CFBridgingRetain(SecCertificateCopyData(certificate))!
    let cerPath: String = NSBundle.mainBundle().pathForResource("xyz.com", ofType: "cer")!
    let localCertificateData = NSData(contentsOfFile:cerPath)!

        if (remoteCertificateData.isEqualToData(localCertificateData) == true) {
            let credential:NSURLCredential = NSURLCredential(forTrust: serverTrust)

            challenge.sender?.useCredential(credential, forAuthenticationChallenge: challenge)

            completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential, NSURLCredential(forTrust: challenge.protectionSpace.serverTrust!))

        } else {

            completionHandler(NSURLSessionAuthChallengeDisposition.CancelAuthenticationChallenge, nil)
        }
    }
    else if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodClientCertificate
    {

        let path: String = NSBundle.mainBundle().pathForResource("client", ofType: "p12")!
        let PKCS12Data = NSData(contentsOfFile:path)!

        let identityAndTrust:IdentityAndTrust = self.extractIdentity(PKCS12Data);

            let urlCredential:NSURLCredential = NSURLCredential(
                identity: identityAndTrust.identityRef,
                certificates: identityAndTrust.certArray as? [AnyObject],
                persistence: NSURLCredentialPersistence.ForSession);

            completionHandler(NSURLSessionAuthChallengeDisposition.UseCredential, urlCredential);

    }
    else
    {
        completionHandler(NSURLSessionAuthChallengeDisposition.CancelAuthenticationChallenge, nil);
    }
}

 struct IdentityAndTrust {

    var identityRef:SecIdentityRef
    var trust:SecTrustRef
    var certArray:AnyObject
}

func extractIdentity(certData:NSData) -> IdentityAndTrust {
    var identityAndTrust:IdentityAndTrust!
    var securityError:OSStatus = errSecSuccess

    let path: String = NSBundle.mainBundle().pathForResource("client", ofType: "p12")!
    let PKCS12Data = NSData(contentsOfFile:path)!
    let key : NSString = kSecImportExportPassphrase as NSString
    let options : NSDictionary = [key : "xyz"]
    //create variable for holding security information
    //var privateKeyRef: SecKeyRef? = nil

    var items : CFArray?

     securityError = SecPKCS12Import(PKCS12Data, options, &items)

    if securityError == errSecSuccess {
        let certItems:CFArray = items as CFArray!;
        let certItemsArray:Array = certItems as Array
        let dict:AnyObject? = certItemsArray.first;
        if let certEntry:Dictionary = dict as? Dictionary<String, AnyObject> {

            // grab the identity
            let identityPointer:AnyObject? = certEntry["identity"];
            let secIdentityRef:SecIdentityRef = identityPointer as! SecIdentityRef!;
            print("\(identityPointer)  :::: \(secIdentityRef)")
            // grab the trust
            let trustPointer:AnyObject? = certEntry["trust"];
            let trustRef:SecTrustRef = trustPointer as! SecTrustRef;
            print("\(trustPointer)  :::: \(trustRef)")
            // grab the cert
            let chainPointer:AnyObject? = certEntry["chain"];
            identityAndTrust = IdentityAndTrust(identityRef: secIdentityRef, trust: trustRef, certArray:  chainPointer!);
        }
    }
    return identityAndTrust;
}

在info.plist文件中完成的更改

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>amazonaws.com.cn</key>
        <dict>
            <key>NSIncludesSubdomains</key>
            <true/>
            <key>NSThirdPartyExceptionRequiresForwardSecrecy</key>
            <false/>
            <key>NSThirdPartyExceptionMinimumTLSVersion</key>
            <string>TLSv1.0</string>
        </dict>
        <key>amazonaws.com</key>
        <dict>
            <key>NSIncludesSubdomains</key>
            <true/>
            <key>NSThirdPartyExceptionRequiresForwardSecrecy</key>
            <false/>
            <key>NSThirdPartyExceptionMinimumTLSVersion</key>
            <string>TLSv1.0</string>
        </dict>
        <key>xyz.com</key>
        <dict>
            <key>NSExceptionAllowsInsecureHTTPLoads</key>
            <true/>
            <key>NSTemporaryExceptionMinimumTLSVersion</key>
            <string>TLSv1.2</string>
            <key>NSRequiresCertificateTransparency</key>
            <false/>
            <key>NSIncludesSubdomains</key>
            <true/>
        </dict>
    </dict>
    <key>NSAllowsArbitraryLoads</key>
    <false/>
</dict>
</plist>

我有同样的问题与iOS9和xcode 7只是补充：

<key>NSAppTransportSecurity</key> 
<dict> 
    <key>NSAllowsArbitraryLoads</key> 
    <true/> 
</dict>

到plist文件。它正在工作，但在您可以实现TLS 1.2之前，它是一个临时的解决方案。