After upgrading my project to iOS7

when I do a BACK Button and the UINavigationControl
This might help you..You can try adding UIViewControllerBasedStatusBarAppearance key and set it's value NO in your info.plist
UIViewControllerBasedStatusBarAppearance = NO
You might try setting the new property on UIViewController edgesForExtendedLayout to UIRectEdgeNone.
Here is a good resource that explains more about how view layouts changed in iOS 7.
See Apple Documentation
If you plan to be backwards compatible you will probably need to do some runtime checks and adjust positioning if the device is not running iOS 7.