When the star sensor is operating in space, it is easy to be interfered by stray light such as sunlight, moonlight and earth-air light. As a result, the overall gray level of the star map taken is increased, the background uniformity is poor, and it is difficult to accurately extract the star coordinates. Aiming at the above problems and combining with the existing algorithms, a composite background estimation star map processing algorithm under stray light interference is proposed. First of all, star points have the characteristics of diameter 3x3 to 7x7 after point diffusion imaging, and the corresponding background estimation template is designed. Then, in order to improve the robustness of the algorithm and improve the utilization rate of local information, a pixel estimation template is designed. The two estimation templates calculate the post-processing data at the same time to achieve threshold segmentation, and then the centroid of star points is calculated. This method can better resist stray light interference and improve the accuracy of star extraction under stray light background.