A distributed Bragg reflector (DBR) for space GaInP/(In)GaAs/Ge triple-junction solar cell is designed by the optical film design software (TFCalc). The experimental results show that the reflectivity of 15-pair Al0.2Ga0.8As/Al0.9Ga0.1As DBR is 96% at the center wavelength of 850 nm. The light in the spectral range of 800-900 nm is reflected and then absorbed twice, which enhances the anti-radiation ability of the middle subcell. According to the detailed balance principle and p-n junction formation mechanism, the thicknesses of the original cell structure and the new cell structure containing the DBR are optimized. By comparing the external quantum efficiency (EQE) of the original cell structure with middle subcell thickness of 2.93 μm and the new cell structure with middle subcell thickness of 1.2, 1.6 and 2.0 μm, we conclude that the influence of the battery current attenuation by thinning base can be almost made up by the new structure. By analyzing the electrical properties of the two types of solar cell structures before and after irradiation, we find that the DBR structure significantly improves the decay of the current after irradiation. The efficiency of the new structure with the middle subcell thickness of 1.6 μm is up to 24.87%, which is increased by nearly 2% than that of the original structure,close to that of the new structure with the middle subcell thickness of 2.0 μm, and significantly higher than that of the new cell structure with middle subcell thickness of 1.2 μm.