The principle and a signal conditioning circuit of tetra-lateral 2-dimensional position sensitive detector（PSD） are analyzed.The experimental calibration system is built in a multipurpose instrument microscope for reducing the position detecting error of this sensor.Based on the error theory

the measuring datum in direction X and Y of the PSD are calibrated in separately area A and B.Experimental results show that the position detection error of the PSD can be reduced by using this method

and the position detection error in area A is no more than（±0.02 mm）.