In this work, a four-terminal AlxGa1-xAs/CuInGaSe2 tandem structure has been proposed by analytical model. To develop this model, the real experimental data for CIGS and AlxGa1-xAs cells has been used. Conversion efficiency of optimized Al0.42Ga0.58As/CuInGaSe2 tandem solar cell achieved to 37.1%. Our model estimates the optimum bandgap of AlxGa1-xAs as top cell is in the range of 1.85–2 eV. The optimized thickness of Al0.31Ga0.69As in tandem structure is 5 μm, which decreases to 0.5 μm by light trapping technique. Moreover, we extended our model by the consideration of threading dislocation density in AlxGa1-xAs layer.