In this study, an optical system of total-reflection night-light remote sensing is designed using the off-axis three-mirror optical structure of COOK TMA based on the development requirements of the urban night-light remote sensing cameras. Its field of view is 5°×2°, focal length is 500 mm, F number is 3.8, and working waveband is 0.4-0.8 μm. The optical axes of the primary, second, and third mirrors are designed to be coaxial to improve the feasibility of optical installation and adjustment. Initially, the appropriate initial structural parameters are selected. Then, ray tracing and optimization are performed using the CODE V software. Results show that the root-mean-square diameter of the spot is 2.305 μm, which is less than one eighth of a pixel. Further, the optical modulation transfer function is greater than 0.92 at Nyquist frenquency of 25 lp/mm, which is close to the diffraction limit. The external baffle, blocking rings, diaphragm, and matte paint are used to decrease the stray-light level. Subsequently, the stray light of the optical-mechanical system is simulated and analyzed using the Tracepro software. The results denote that the point source transmittance is between 10 ^-11 and 10 ^-3 when the off-axis field of view is 1°-80°. Furthermore, the point source transmittance is less than 1×10 ^-9 when the solar suppression angle is 65.96°-80°, which satisfies the application requirements.