According to the imaging process of star over saturation phenomenon, the characteristics of Point Spread Function (PSF) of star image points are analyzed, and the energy distribution model of over saturation star image is established, and a PSF correlation algorithm is proposed. The algorithm first identifies the PSF sequence with the best star regional similarity, positioning by finding the maximum value of the sequence. Simulation experiments show that the positioning error of the PSF correlation method is as low as 0.05 pixels under the condition that the star image points are noisy. Under the asymmetric PSF condition, the positioning error is still less than 0.1 pixels, which is higher than the traditional centroid method, surface fitting method and other methods.