Abstract: A flexible thin-film GaInP/GaAs/InGaAs inverted metamorphic triple-junction (IMM3J) solar cell with conversion efficiency up to 32.47% (air mass (AM) 0, 1 367 W/cm2) was prepared to meet the requirements of space solar cells for lightweight and high efficiency. Highenergy proton radiation (1, 3 and 5 MeV) was carried out to study its antiirradiation performance. The SRIM simulation models indicate that 1, 3 and 5 MeV proton irradiation will cause approximately uniform damage in IMM3J cells. The light IV (LIV) results show that the degradation of the opencircuit voltage (Voc), shortcircuit current (Isc) and maximum output power (Pmax) follows the logarithm change of the proton fluence. The fluences of different energy protons were converted into the displacement damage dose (DDD) through nonionizing energy loss (NIEL). The Voc and Pmax decrease with an approximative logarithmic change of DDD, while the Isc follows two different degradation behaviors. The spectral response tests prove that GaInP sub-cell has excellent anti-irradiation performance, but InGaAs (1.0 eV) sub-cell has the worst anti-irradiation resistance and is the currentlimiting subcell during the 1, 3 and 5 MeV protons irradiation continuously.