Abstract: GaInP/GaAs/Ge triple junction solar cells have the advantages of high reliability, long life, and high photoelectric conversion efficiency, making them the core components of current spacecraft space power systems. However, the radiation particles in the space environment interact with solar cells and cause displacement damage, leading to the electrical parameters of the solar cells to attenuate, and even causing the failure of spacecraft power supply system, seriously affecting the mission of spacecraft in space. In order to achieve the degradation of the GaInP/GaAs/Ge triple junction solar cells induced by high energy protons, the domestic GaInP/GaAs/Ge triple junction solar cells were taken as the research object, and the radiation experiments of 100 MeV protons under different fluencies were carried out. The experimental results and damage mechanisms of sensitive parameter degradation induced by proton displacement damage in triple junction solar cells, such as open circuit voltage (V_oc), short circuit current (I_sc), maximum output power (P_m), and photoelectric conversion efficiency (E_ff), were analyzed. In order to better analyze the damage caused by 100 MeV protons to the GaInP/GaAs/Ge triple junction solar cells, the transport process of protons was simulated by Geant4 software. The information of the primary knocked-on atoms (PKAs) was obtained by judging the interaction between particles and materials in the transport process. By analyzing the distribution of PKAs in the depth of the GaInP/GaAs/Ge triple junction solar cells caused by 100 MeV protons, it is found that 100 MeV protons can cause uniform displacement damage throughout the entire triple junction solar cell. The above electrical parameters of GaInP/GaAs/Ge triple junction solar cells were tested and analyzed before and after proton irradiation under AM0 and 25 ℃ conditions. The experimental results show that the degradation degrees of normalized V_oc, I_sc, P_m, and Eff increase with the increase of proton fluence when the fluence range is 1×10¹¹-2×10¹² cm^-2. When the proton fluence is 2×10¹² cm^-2, the degradation degrees of normalized V_oc, I_sc, P_m, and Eff are 8.94%, 3.34%, 16.88%, and 16.88%, respectively. By fitting the degradation degrees of normalized V_oc, I_sc, and P_m obtained by irradiation with different proton fluences, the characteristic curves of these three electrical parameters changing with the proton fluence are obtained. Based on these curves, the attenuation amplitude of the GaInP/GaAs/Ge triple junction solar cell performance under other fluences can be estimated. According to the fitting curves of V_oc, I_sc, and P_m, it can be seen that Pm always attenuates most seriously under the same proton fluence.