When a Cassegrain telescope system is taken as optical antenna, the error of annular facula position detection on the photosensitive surface of four-quadrant photoelectric detector in acquisition, pointing and tracking system for atmospheric laser communication is analyzed. Based on the equivalent effects of the facula center shelter and dead zone induction light energy, mathematical models of relationships among facula center coordinate, dead zone width of detector, inner and outer circle radii of annular facula and incident annular facula offset are theoretically deduced. Numerical simulation and experimental results show that the detection linear range of annular spot is smaller than that of complete Gauss facula, and the detection sensitivity is lower. The appropriate Cassegrain optical antenna and facula radius are selected according to the experimental conditions, so that the detection linear range of detector is the largest when the shading ratio is 30%, and nonlinear error will not occur. An annular facula error compensation algorithm is proposed to overcome the position detection error caused by the facula center shelter, and the detection accuracy of the detector can reach 0.0015 mm.