In this paper, the degradation related parameters of GaInP/GaAs/Ge triple-junction solar cell induced by electron irradiation are carried out by numerical simulation. The degradation results of short-circuit current, open-circuit voltage, maximum power have been investigated, and the degradation mechanism is analyzed. Combining the degradation results, the degradation of normalized parameters versus displacement damage dose is obtained. The results show that the degradation increases with the increase of the electron fluence and electron irradiation energy. The degradation normalized related parameters versus displacement damage dose can be characterized by a special curve that is not affected by the type of irradiated particles. By calculating the annual displacement damage dose and the on-orbit operation time of special space orbit, the degradation of normalized parameters can be obtained with the fitting curve in the simulation. The study will provide an approach to estimate the radiation damage of triple-junction solar cell induced by space particle irradiation.