Solar thermal propulsion is a high efficiency propulsion system, utilizing concentrated sunlight radiation to heat low molecular weight working fluid and providing high specific impulse. With regenerative cooling, an integration of the second concentrator and thruster can cool down the former to 1600K and preheat the propellant to 600K, thus improving the energy conversion efficiency of the propulsion system. The thermal radiation simulation shows that the flowing propellant is of little influence on the cavity temperature and the cavity can maintain high temperature between 2400K and 2600K.