To solve the problem of inconsistent grayscale in single-band image after stitching of multi-spectral images of filter array, a new method of the mean tuning algorithm for the mean ratio of grayscale in overlapping regions of each band is proposed. Firstly, multi-spectral image template is constructed based on the effective region of each band, the projection transformation of the multi-spectral image and the image template is carried out using the platform posture information, and the SURF(Speeded Up Robust Features) algorithm is used to extract image matching points and calculate the homography matrix between adjacent images, the intermediate sequence image is selected as the reference image to register the projected image and image template; secondly, the mean value of the ratio of the grayscale averages in overlapping areas of each single-band image after projection is used as the image grayscale adjustment coefficient, and the reference image is used as a reference to adjust the grayscale of the aligned image in turn; finally, each single-band sequence image is obtained by using the grayscale adjusted multi-spectral image and the aligned image template, the large area single-band image with consistent grayscale is obtained by image stitching. Theoretical analysis and experimental results show that this method can effectively solve the problem of filter array multi-spectral image grayscale inconsistency, and then maintain the spectral information characteristics of the features in different wavelength bands to the maximum extent.