The invention provides an optical touch display device. The optical touch display device comprises a display module, a first image capturing module, a second image capturing module and a processing module. The display module generates N touch points according to a touch gesture, the touch gesture has a specific moving model, and N is a positive integer. The first image capturing module retrieves a first image relating to N touch points. The second image capturing module retrieves a second image relating to N touch points. The processing module determines correspondingly a specific touch chord of N touch points according to the first image and the second image, and determines correspondingly a specific function of the touch gesture according to the specific touch chord and the specific moving mode.