Abstract: The thermal control problem of minisized-electromotors in a lunar detector was analyzed. Based on the actual parameters of some minisized-electromotors, a thermal control system using an umbrella-like radiation cooling surface was conceived. The key influencing factors, such as the operating torque of the minisized-electromotors, lunar surface temperature, lunar latitude, etc., were considered. And the variations of the thermal states of the system with the above-mentioned factors were simulated. The results show that, with the proposed thermal control system, the minisized-electromotors temperature can be controlled in the allowed upper limit of the lunar environment.