Abstract: In this paper, through theoretical arithmetic and experiments, we develop the position resolution to the beam in coarse-tracking subsystem of spatial optical communication that used PSD From the experiments, when the power of the beacon beam on the photosurface of the PSD is about 2.8μW,the spatial position resolution is about 12.6μm Meanwhile, through computer simulation and experiments, we have compared the experimental data and the theoretical data of the linearity of PSD.