The invention belongs to the optical precision test technology field and particularly relates to an optical system for a solar telescope. The system comprises a main mirror, a heat diaphragm, a field diaphragm, a collimation lens, a reception lens and an image plane. The system is characterized in that the field diaphragm is an arc-shaped structure, the surface of the field diaphragm facing the incidence light is coated with a reflection film, and a problem that failure of high-resolution task observation caused by influence of stray light flooding on field signals because of great heat accumulated on the field diaphragm is solved.