1. A touch object separating method of an optical touch system, adapted to the optical touch system having a first lens, a second lens and a screen, wherein the first lens and the second lens are disposed on the same side of the screen and face toward another side of the screen, the method comprising: recognizing at least one touch object image in a first captured image and a second captured image captured by the first lens and the second lens; when the first captured image comprises two touch object images and the second captured image comprises a single touch object image, calculating a first distance between a leftmost end and a rightmost end of the two touch object images in the first captured image, a second distance between centers of the two touch object images, and a third distance between a leftmost end and a rightmost end of the single touch object image in the second captured image; calculating a fourth distance corresponding to the third distance according to a ratio of the first distance to the second distance; and separating the single touch object image into two touch object images according to the forth distance, and combining with the two touch object images in the first captured image and the separated two touch object images in the second captured image to calculate positions of two touch points of the at least one touch object touching the screen.