In order to realize the synchronization of two images urgently, effectively reduce the transmission load, the double image encryption algorithm based on coefficient fusion model and saw tooth filling curve was proposed in this paper. Firstly, the coefficients matrix of the input plain was obtained by discrete cosine transform DCT and Zigzag scanning mechanism, and the two plain matrix is transformed into a fusion matrix by constructing the coefficient fusion model, then the composite image was obtained by inverse discrete cosine transform. Subsequently, the design of the zigzag filling curve, the pixel location of the composite image to disturb the formation of scrambling image. Finally, the improved gravity model, the scrambled image diffusion, changes the gray value. The experimental results show that the algorithm can be used to encrypt the two images simultaneously, and it has high security and no loss of information.