Abstract: Electrostatic interaction plays an important role in the binding of HIV-1 protease and ligand. Understanding the role of this interaction may assist designing better drugs targeting on HIV/AIDS disease. In this work, we have applied the Poisson – Boltzmann method to calculate the binding electrostatic energy between HIV-1 protease and lopinavir. The results imply that the inhibitor binds stronger to 2Z54, 2O4S, 2RKF and 2RKG mutants and weaker to 2QHC and 2Q5K. The potential maps of 2RKG and 2RKF are more negative than the others. These results can be used along with molecular dynamics calculation to give more precise evaluations on the binding between drug and different HIV-1 protease mutants.