Is there any auto-called function when usb cable plugged in just like applicatonDidBecomeActive?
[edited]: Yes, well sort of. If you enable battery monitoring ([UIDevice currentDevice].batteryMonitoringEnabled = YES) then you can query for the battery state ([UIDevice currentDevice].batteryState) and if it is UIDeviceBatteryStateCharging or UIDeviceBatteryStateFull, then the device is plugged in. You would have to poll for this, though, since as far as I know, there isn't any sort of notification that alerts when the state has changed.
I'm now working with box2d and when I plugged usb cable in, b2bodys got bumped and crashed so I might have to pause when it plugged in,
I'm confused, so your game crashes when you plug in the USB cord? If so, then that has nothing to do with Box2D, and you should probably look into the root of the problem.