Structured illumination microscopy has been a useful method for achieving lateral super-resolution, but it typically requires at least three precise phase shifts per orientation. In this paper, we propose a super-resolution method that utilizes structured illuminationwithout phase shift. The reconstruction process requires only a conventionally illuminated image and an image with structured illumination. This method achieves the same effect as the traditional phase shift method, and more than doubles the resolution by synthesizing a few reconstructions at different illumination frequencies. We verify the resolution improvement process using a combination of theoretical derivations and diagrams, and demonstrate its effectiveness with numerical simulations.