The position sensitive photomultiplier tube(PSPMT)was introduced to the experimental measurement of laser beam wandering induced by atmospheric turbulence. Based on the operating principle of PSPMT,the effect of the detector's placement to the output signal was analyzed. The position and gain calibration was experimentally performed in order to obtain the position coordinates of the incident light in the active area of PSPMT. The experimental measurements show only one sample can't express the position of the incident light correctly when the light is strong and the beam width has the order of centimeter. So the statistic mean position of some samples for the same incident light was used to denote the real incident position. The highest sampling rate and sampling points combined with signal frequency were taken into account to determine the number of sampling points to be averaged.