A touch display device includes a touch panel, a driving and sensing circuit, a data memory, a processor and a display apparatus. The touch panel is adapted to receive a touch trace including at least one touch point. The driving and sensing circuit is adapted to detect an actual signal value Vi of the at least one touch point. The data memory is adapted to store a look up table including a plurality of position coordinates and calibrating rules f each corresponding to each of the position coordinates and can be used to convert actual signal value V0i of a basic contact area A0 to a standard signal value Vs. The processor is adapted to calculate the position coordinate and calibrate the actual signal value Vi to a calibrated signal value V′i. The display apparatus is adapted to display the touch trace.