To remove the random noise and low-frequency coherent noise in the images of 4f coherent optic image processing system, a method based on fusion of multiple spatial frequency spectrum images is proposed. Firstly, capture the multiple spatial frequency spectrum images of once experiment based on the image copying character form the lattice structure of spatial light modulators. These images contain the same useful image information and noise with the similar distribution but different values. Then, these images are combined by image fusion algorithm whose principle is approximate to the time-domain cumulative mean method to remove the noise. The theoretical analysis and physics experiments show that the method can remove the random noise and diluted the low-frequency coherent noise well, and almost no harm to the useful image information.