The parameters of the window layer and intrinsic layer of the ultrathin heterojunction solar cells were simulate and optimize with AFORS-HET software, such as doping concentration, thickness and band gap, et al. The influence law of each parameter on the performance of the ultrathin heterojunction solar cell was analyzed in combination with the actual situation, and the optimal optimization parameters were obtained. The simulation results show that: for the ultrathin heterojunction solar cell with substrate thickness of only 80 μm, with the increase of the thickness of the window layer, the overall performance of the cell shows a trend of decline. According to the practical situation, the optimal thickness range of the window layer is 5 nm to 9 nm. With the increase of the doping concentration in the window layer, the cell performance as a whole increases first and then tends to be constant. The optimal doping concentration range of the window layer theoretically is 7×1019 to 8×1019.The band gap width of the window layer has a great influence on the open-circuit voltage and efficiency of the battery, but has a small influence on the filling factor and short-circuit current. The optimal band gap range of the window layer is 1.85 eV to 2.0 eV.With the increase of the thickness of the intrinsic layer, the FF and efficiency of the cell first increases and then decreases. The short-circuit current gradually decreases while the open-circuit voltage remains basically unchanged. The optimal thickness of the intrinsic layer is 5 nm to 10 nm.When the optical band gap of the intrinsic layer is less than 1.8 eV, it has little influence on the battery performance; when the optical band gap of the intrinsic layer is more than 1.8 eV, the cell performance drops sharply. Therefore, the optimal band gap range of the intrinsic layer is 1.6 eV to 1.8 eV.