Abstract: The binding pattern of human serum albumin (HSA) and cypermethrin was investigated by AutoDock molecular docking, molecular dynamics, binding free energy calculation and alanine scanning mutagenesis. The results showed that HSA and cypermethrin could lead to stable complex. And one hydrogen bond between cypermethrin and amino acid residue Arg209 was formed. The binding free energy was –83.43 kJ/mol. The van der Wals force was the main driving forces and the polar solvation energy was the main resistance force of the binding. ΔΔG_bind of Lys199 was 16.78 kJ/mol through alanine scanning mutagenesis calculated, which was the key amino acid in the combination between HSA and cypermethrin. These results could provide theoretical references to illustrate the metabolism mechanism of cypermethrin in human body.