Abstract: In order to encrypt double color images in a single channel, firstly, two color images to be encrypted were converted to indexed images instead of RGB model and the color mapping matrix of the index images was reserved. Then, after the logarithm operation, fraction Fourier transformation and random modulation of the data matrix, both the images were encrypted. The theoretical analysis and experiment results indicate that two color images can be retrieved without distortion only when correct keys are used. The algorithm has high security.