The irradiation effects of 0.28-2.80 MeV protons on GalnP/GaAs/Ge solar cells have been analysed, and then correlated with the displacement damage dose. The results of Ⅰ-Ⅴ and spectral response measurements, combined with the SRIM-derived vacancies produced rates, show that the degradation of the solar cells is largely determined by the displacement damage of the GaAs sub-cell. Thus the SRIM-derived NIEL values for protons in the GaAs sub-cell are used to calculate the displacement damage dose. It is shown that the irradiation effects of the solar cells caused by protons at different energies are correlated well with the aid of displacement damage dose.