ATP is a key technology in optical communication system. There are three optical-electornic detectors used commonly: PSD (Poistion-Sensetive Debices), QD(Quadrant Detector) and CCD (Charge-Coupled Devices), among these detectors, the simplest, the most excellentest and the commonest is the QD. In this paper, we analysis and investigate explicitly the performance of QD in detection technology.