Accurately estimating the spatial position of the interaction between the ray and the detector in radiation imaging is a key step to ensure the imaging quality. To further improve the position effect of radiation events and effectively suppress the position shift caused by the center of gravity method when radiation events are close to the edge of the detector, a response function-based position algorithm is established for the position -sensitive detection system composed of Si-PM arrays. A position-sensitive detector based on CsI array and Si-PM array and an ASIC-based electronic readout system were built, and the equivalent resistance network was used to simplify the number of output signals of Si-PM array, then the response functions of radiation events on Si-PM arrays were obtained experimentally. The experimental results show that under the same conditions, the FWHM of the scatter points of the most edge pixels using the response function method is only 46.2% of the FWHM obtained by using the center of gravity method, which is comparable to the FWHM of the scatter points of the central pixels, the localization effect of the radiation event method based on the response function is obviously better than that of the traditional center of gravity method, which can effectively overcome the edge effect of the center of gravity method.