A geometry optical model for analyzing the influence of earth albedo on star tracker is presented.Based on the principle of photometry and Point Source Transmittance（PST）,this model has a certain generality and practicability by means of dividing earth surfaces into 2D cells with longitude and attitude and providing application interface of available TOMS reflectance data.It can be used to analyze the magnitude of irradiance of entrance and exit of a sunshade and corresponding imaging surface at different off-axis angles,where earth albedo pours on within some conditions,including altitude of orbit,installing position of star tracker,incident angle of sun,etc.Based on this model,we can make proposal of installing orientation of star tracker on satellites and estimate anti-earth albedo performance of sunshade of star tracker.Simulation indicates that for MEO and LEO,the irradiance of earth albedo reaching the entrance of sunshade of star tracker changes little,the magnitude of irradiance of earth albedo received by the exit of sunshade is mainly related to its PST and installation elevation;When this angle is equal to 32.5°,the irradiance of the exit of sunshade declines to 10-7 W/m2,thus satisfying sunshade′s requirement of suppressing stray light.