Abstract: The performance degradation of GaAs solar cells under the conditions of space radiation is closely related to the microstructure of the cells. Based on the molecular dynamics, this paper studies the collision cascade process caused by the PKA, generated by the protons in the spatial capture zone and with different energies(0.1 to 10 keV). We analyze the evolution of the defects against the time and the energy of the PKA, as well as the formation characteristics of the point defects and the defect clusters. A certain linear relationship is shown to exist between the number of Frenkel pairs and the PKA energies at the "displacement spike" and in the steady state; the higher the PKA energy is, the more serious the radiation damages will be, and the defects are harder to recover, but the recombination rate of the defects tends to saturate; the point defects in the GaAs exist mainly in the form of defect clusters, and with the increase of the PKA energy, the isolated defects tend to associate with the defect clusters.