Abstract: An optical system having a secondary mirror refocusing mechanism includes a primary mirror; a secondary mirror arranged corresponding to the primary mirror, and the secondary mirror is smaller than the primary mirror; a mirror base for receiving the secondary mirror; a beam having a first end and a second end disposed opposite to each other; and an actuation mechanism including a thermal deformation structure and a heating device, the heating device provides thermal energy to the thermal deformation structure such that the thermal deformation structure generates a deformation; wherein, the first end of the beam is fixed to the mirror base, the second end of the beam is fixed to the actuation mechanism, and the beam and the actuation mechanism are deformed correspondingly. With the above structure, the secondary mirror can be refocused to ensure the imaging quality of the optical system.