Abstract: To investigate the radiation heat transfer characteristics of liquid sheet radiator in space reactor system, the geometric and physical model was established with STAR-CCM+. By changing the geometry size, shape, transmitting temperature, and working fluid of the liquid sheet, the numerical calculation was conducted and radiation heat transfer characteristic was analyzed. It can be concluded that in the rectangular liquid sheet, the heat rejection power per unit mass increases with the radiation area per unit mass. For the shape, liquid sheet can achieve better radiation heat transfer performance, as rectangle and triangle with same area have more room to change shape. The radiation heat transfer performance can be improved and the mass of liquid sheet radiator can be reduced by increasing the transmitting temperature. However, high temperature also accelerates evaporation of the working fluid. The working fluids with small density and high emissivity have better performance. Considering the factors of evaporation and economics, liquid tin is a better choice as working fluid at high temperature. The research result provides theoretical support and scientific basis for the optimization design of space liquid sheet radiator.