In order to extend the detection range of position sensitive detector, solve the problem that the light spot cannot be accurately positioned when the light spot is off-target on the PSD photosensitive surface, a light spot off-target error compensation method is proposed. The variation law of the spot energy center of PSD detection before and after the off-target was analyzed, and the functional relationship between the PSD light intensity signal and the position detection error was established. The experimental results show that: when the size of the PSD photosensitive surface is 12mm×12mm, the Gaussian light spot with a radius of 5mm is used, and the X-axis detection range of the PSD photosensitive surface is increased by 66.7% after compensation by the spot compensation method proposed in this paper, and the average relative error of position detection is no more than 5%.