Atmosphere turbulence is one of the main causes of degraded image quality in the area of detecting space objects based on optical telescope on earth. Atmosphere turbulence results in distortion of wavefront, and it causes different kinds of blurred images. In order to recover original images from blurred images, a method to evaluate point spread function based on atmosphere coherent length is proposed, and the theoretical formula is deduced. Sobel method is used to evaluate the image qualities of recovered images after same times of blind convolution, and the value of atmosphere coherent length is found out when the value of image quality is maximal. This atmosphere coherent length is applied to point spread function and the restored image is got after blind convolution. With many kinds of image quality evaluation indices, it is proved that this method can make us get a good restored image without measuring the value of atmosphere coherent length.