The present invention discloses a tablet computer and a method for controlling the same. The method includes steps of receiving a first video signal outputted from an external device; converting the first video signal into a first low voltage differential signal; receiving a second video signal outputted from a processor; converting the second video signal into a second low voltage differential signal; making the tablet computer selectively operate in a tablet computer mode or an external device mode; outputting the second low voltage differential signal to a display module to display corresponding data when the tablet computer operates in the tablet computer mode; and outputting the first low voltage differential signal to the display module to display corresponding data when the tablet computer operates in the external device mode.