两个storyboard，多个storyboard 引用，代码调用

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
        /// 获取两个Tab对应的 Storyboard
        let story_first = UIStoryboard(name: "First", bundle: nil)
        let story_second = UIStoryboard(name: "Second", bundle: nil)
        /// 获取Tab 对应的第一个 ViewController
        let first_nav_viewcontroller = story_first.instantiateViewControllerWithIdentifier("first-nav") as UINavigationController
        let second_a_viewcontroller = story_second.instantiateViewControllerWithIdentifier("second-a") as SecondAViewController
        /// 设置 tabBar 内容
        first_nav_viewcontroller.tabBarItem = UITabBarItem(title: "First", image: nil, tag: 0)
        second_a_viewcontroller.tabBarItem = UITabBarItem(title: "Second", image: nil, tag: 1)
        /// 为我们的 UITabBarController 设置对应的两个ViewController
        self.viewControllers = [first_nav_viewcontroller, second_a_viewcontroller]
    }