In the optical design stage, tolerance sensitivity control is undoubtedly a very important link. It determines the processing cost of the lens, and the imaging quality of the final product. Based on the geometric aberrations theory, a large-aperture industrial lens is designed by Zemax. The tolerance analysis shows that some surfaces of the behind group have very high tolerance sensitivity. By writing a special ray tracing program, the reason of why the tolerance of optical system is sensitive have been found. In order to reduce tolerance sensitivity, the method of optimization aperture angle is put forward. According to the relationship between senior aberration and aperture angle, the optimized value of aperture angle is found. The results show that this method can effectively control the tolerance sensitivity.