Heterojunction with intrinsic thin-layer (HIT) solar cells have attracted a great deal of interest in the researchers recently due to its advantages of high energy conversion efficiency and low temperature production procedure, however the high cost of raw material, the harsh technical conditions and the defect state control have become the major problems which prevent its further development. The AFORS-HET software is employed to simulate the influence of the absorber layer doping concentration, the defect density and the interface defect density of state on the ZnO(n)/ZnSe(i)/c-Si(p) heterojunction solar cell’s performances (the short-circuit current, open-circuit voltage, fill factor and photoelectric conversion efficiency). The optimized result shows that when the doping concentration of the absorber layer is 1×1021 cm-3, the defect density of the ZnO layer and c-Si layer is less than 1017 cm-3, and the defect density of the ZnSe/c-Si interface is less than 1025 cm-3, the photoelectric conversion efficiency of the solar cell with this structure can reach 24.29%.