A four-junction InGaN-based multijunction solar cell structure is proposed theoretically. The simulation results show that, with the use of appropriately designed compositional grading layers, the performance of InGaN-based multijunction solar cell can be maintained without the cost in performance degradation caused by the polarization-induced electric field and the potential barriers resulting from the heterointerfaces. After the optimization in thicknesses for current matching, a high conversion efficiency of 46.45% can be achieved under 1000-sun AM1.5D illumination, in which the short-circuit current density, open-circuit voltage, and fill factor are 12.2×10 3 mA/cm 2 , 4.18 V, and 0.77, respectively. The simulation results suggest that, in addition to the detrimental effects caused by the built-in electric polarization and potential barriers, the issue of crystalline quality is another critical factor influencing the performance of multijunction solar cells.