A simple model of the graded heterojunction in ALGaInP compound semiconductors was introduced to analyze the energy band profile.We analyze the energy band profiles with the different grading ways but the same grading length,under the different doping densities.We analyze the effect of the different grading lengths on the surplus of the spike potential to the potential of the n region under the different doping densities.We analyze the effect of the graded heterojunction,finding it can improve the HB-LED (high-brightness light emitting diode)performance,and proved by the experiment.A graded heterojunction should be applied to HB-LED,based on this analysis.