Abstract: This paper introduces a position sensitive detector and a non contact position detection system.The system include a laser diode light source,a imaging optical system and a image position sensitive detector.The surface of a body is illuminated with the light source and imaged on the sensitive surface of the detector.According to the relationship between the body and its image,the deviation of the body can be calculated.The measurement accuracy of the deviation depends on the position discriminativity.In our system,the position discriminativity of the detector is 2 micron,the measurement error is less than 5 micron.