In this paper,the degradation of irradiated GaAs/Ge single junction (SJ) solar cells is evaluated under the orbital environments using the displacement damage dose method. Firstly the electric-property changes of the SJ solar cells are experimentally obtained with the fluencies of electrons and protons of various energies under ground-based irradiation simulators. Based on the experimenal results and the calculated non-ionization energy losses (NIELs) of the electrons and protons in GaAs, the equivalent exponent n is obtained to be 1.7 for various electron energies,while the equivalent coefficient Rep for electron displacement damage converted into that of protons is 5.2. Furthermore, a degradation formula of the electrical property of the domestic SJ solar cell is established as a function of displacement damage dose during the particle irradiation. Using the displacement damage technique, the orbital evolution of the electric property degradation of the domestic SJ cell is predicted in this paper. In the meantime, the shielding effects of the cover glass with different thicknesses are also evaluated.