Radiation damages of 1 Mev and 1.8 Mev electrons to the triple-junction GaInP/GaAs/Ge solar cell are investigated. The results indicate that electric properties of the GaInP/GaAs/Ge triple-junction solar cell, such as open-circuit voltage, short-circuit current and maximum power, decrease obviously as the irradiation fluence increases. Under the irradiation fluence of 1×1015cm-2 of 1 MeV electrons, the maximum power output is degraded by 17.7%. Under higher energy electron irradiation, the dark I-V characteristic shows that the changes in both the series and parallel connection resistance of the triple-junction cell are reasons causing the degradational of electrical properties. By the analysis of spectral response, the degradation in electric properties is primarily duc to the severe damage of the GaAs sub-cell. The damage of the sub-cell is associated closely with the obvious decrease in the collecting efficiency of light-generated carriers in the bottom of the base-zone. The key to improve the radiation resistance of the triple-junction GaInP/GaAs/Ge solar cell is to reduce the damage of the base-zone of GaAs sub-cell as much as possible.