Spacecraft have to be exposed to complex and harsh space radiation environments for a long time during their in-orbit service. III-V compound solar cells, represented by GaAs, are widely used in the aerospace field due to their high photoelectric conversion efficiency and radiation resistance. The spatial radiation damage effect of GaAs solar cells was studied using finite element method and technology computer-aided design (TCAD). Based on the electrical parameters of GaAs solar cells under AM0 spectral irradiation, a single-junction solar cell structure model and irradiation damage model were established. The volt ampere characteristic curves of the cells under different electron irradiation conditions were obtained, and the simulation results in this paper were verified with existing experimental results. The degradation law of GaAs solar cell electrical performance under space environment irradiation was analyzed. The results indicate that irradiation damage defects reduce the diffusion length of minority carriers and decrease the collection efficiency of photo generated carriers. At a certain electron energy, the degradation amplitude of the electrical performance of solar cells increases with the increase of irradiation dose level.