Abstract: In order to meet the requirements of on-orbit maintenance of large orbital replacement units (ORU) on the space station, a clutch impact mechanism of extravehicular power tool with low rotation speed, large torque output, small reaction force, and low impact vibration was developed. By establishing a differential equation of motion, the key motion state of the impact mechanism in a single collision period was analyzed, and the torque control equation of stable operation process was derived. The influence of key design parameters of impact mechanism on ultimate impact torque was studied, and the structural transient dynamic simulation was carried out based on the design results. The on-orbit maintenance ground simulation test platform and extravehicular activities(EVA) simulator were set up to carry out the functional verification test and ergonomic test of impact power tool. The results show that the reaction force and vibration amplitude of the subject’s hand are rather small, and tightening torque produced by the tool can be as large as 41.64 N · m, enough for tightening and loosening M10 screws. The research may provide technical support for the development of the impact tools with high torque output on orbit.