For analyzing land covers and matching of remote sensing images, gray calibration of image is an indispensable part, for the result will directly influence the later procession. An algorithm of image gray calibration based on histogram correlation with linear point operations is put forward in three steps. Firstly, solve the slope ratio by making histogram of image for calibrating and expecting consistency. Secondly, solve the amount of shift by histogram correlation. Thirdly, realize gray calibration by using linear point operations. The result shows that the method has better stability for gray changing caused by illumination.