Abstract: The routine collimation imaging γ camera would produce the gamma image with shrinkage effect if not corrected, due to such factors as scintillator thickness, PSPMT photo cathode thickness and centroid method for calculating photo position. For this reason, a newly developed calibration system was presented in this paper, and the experimental verification was carried out. The system can scan the surface of plate scintillator detector in a point-by-point way so as to obtain the initial informations of both the scanning point position within the effective zone and the response position of the plate scintillator detector. In this way, the information on the realistic position of gamma photo entering the detector and its mirror image shaped from the output circuit can be obtained, so that the position lookup table can be created to restore the realistic position of each photo entering the effective zone of γ camera. As a result, the image distortion arising from gamma imaging that would be unable to be avoided can be effectively reduced. The calibration system is able to create automatically a position lookup table, without manual operation. This provides the necessary conditions for the restoration of pinhole image or/and the reconstruction of aperture-coded image by using gamma camera.