The effects of low‐energy proton irradiation on the electrical property of GaAs/Ge solar cells used in space applications are studied. The protons energy in the experiment was selected in the range of 70∼170 keV with a fluence of up to 3×1012 cm−2. The results indicate that under the experimental conditions, the electrical properties such as the short circuit current (Isc), the open circuit voltage (Voc) and the maximum power (Pmax) of the GaAs/Ge solar cells decrease with increasing proton fluence. Increasing the proton energy can result in more serious damage to the solar cell. The proton irradiation can also reduce the filling factor (Ff) of the I‐V curves of the cells. A mechanism of the irradiation damage of GaAs solar cell is discussed.