The function of spot-detecting camera in satellite-to-ground laser communication acquisition, tracking, pointing (ATP) system is expounded. When defective pixels exist on the detector, the false alarm rate and positioning accuracy of spot-detecting camera will be affected. The kinds and sources of defective pixels on matrix detector are analyzed. The characteristics of spot-detecting camera in satellite-to-ground laser communication ATP system are also analyzed. According to these characteristics of camera, the real time method of defective pixel check and correction is explained. A spot-detecting camera based on STAR-1000 sensor is designed, which also uses the correction method. Some tests are carried out to verify the correction method. The results show that the real time correction method can restrain defective pixels effectively and the gray value of defective pixels will be corrected. Because this method has short delay and it can reduce the positioning error when the camera has defective pixels, it cna well apply to the satellite-to-ground laser communication ATP system.