Requirements of high-precision spot detection in laser communication acquisition, tracking, pointing (ATP) systems are analyzed, and the advantages of selecting complementary metal-oxide-semiconductor (CMOS) sensor are explained. According to the needs, design principles of a spot-detecting camera based on STAR-1000 sensor as well as hardware implementation methods of centroid algorithm are expounded. The positioning accuracy of the camera is affected by some defects, for example noise and limited duty cycle in the CMOS sensor. Several factors in positioning accuracy are analyzed and the effect is simulated. Test results from imaging experiment system formed verify these analyses. According to the experiment designer can improve positioning accuracy by reducing noise, improving duty cycle, and expanding the effective spot diameter. And then, suggestions for improving positioning accuracy are put forward which contrapose laser communication ATP system.