Infrared/millimeter wave (IR/MMW) composite guidance is a hot direction of current development in the field of multi-mode composite guidance technology. In view of the limited penetrability of infrared detection system under low visibility condition and the low resolution of passive millimeter wave detection image we put forward a new MRA-based PCA (M-P) fusion method in order to better fuse the images of IR and the PMMW and to enable the composite seeker with all-weather operations. By using the advantage of multiresolution analysis that it can solve the information according to the resolution of the image space the M-P fusion method denoises the infrared and passive millimeter wave detection tank group images and transforms the reconstructed images with PCA respectively. Then the first principal component of low resolution image is replaced by that of high resolution image. Finally inverse PCA transform is made to obtain the fusion image. The experiment indicates that compared with PCA the new fusion method can better distinguish the tank group objects from the surface features.