Based on a Fourier synthesis illuminator, high frequency MEMS(Micro-electro-mechanical system) vibration micromirror is introduced as an illumination field uniformizing device. In addition to the realization of any off-axis illumination modes, the optimized structure can further improve the intensity uniformity of illumination field and the imaging resolution. It has a simple structure and is easy to operate. The Fourier synthesis illumination and uniformizing structure scheme are designed, the simulation model is established, and the experimental device is set up to verify the uniformity effect through imaging method. In addition, the influences of the vibration amplitude and vibration frequency of the MEMS micromirror on the uniformizing effect are analyzed. The uniformity in the selected illumination area can be increased by more than 11%. The Fourier synthesis illumination and field intensity uniformizing method can be applied to the illumination applications in lithography mask inspection.