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Metamorphic In0.55Ga0.45P/In0.06Ga0.94As/Ge triple-junction (3J-MM) solar cells are grown on Ge (100) substrates via metal organic chemical vapor deposition.Epi-structural analyses such as high resolution x-ray diffraction,photoluminence,cathodoluminescence and HRTEM are employed and the results show that the high crystal quality of 3J-MM solar cells is obtained with low threading dislocation density of graded buffer (an average value of 6.8× 104/cm2).Benefitting from the optimized bandgap combination,under one sun,AM0 spectrum,25℃ conditions,the conversion efficiency is achieved about 32％,5％ higher compared with the lattice-matched In0.49Ga0.51P/In0.01 Ga0.99As/Ge triple junction (3J-LM) solar cell.Under 1-MeV electron irradiation test,the degradation of the EQE and I-V characteristics of 3J-MM solar cells is at the same level as the 3J-LM solar cell.The end-of-life efficiency is ～27.1％.Therefore,the metamorphic triple-junction solar cell may be a promising candidate for next-generation space multi-junction solar cells.