The ACE inhibitory activities of four food-derived tripeptides，including IRP，IKP，GRP and IRA，were verified by some experiments.However，their interaction modes with ACE and molecular mechanism remain unclear.This research focused on resolving the above problems using flexible molecular docking method.The molecular docking results demonstrated that four peptides had similar action modes with ACE.Hydrogen bond，hydrophilic，hydrophobic and electrostatic interactions were together responsible for the conformational stability of the complexes formed by peptides and ACE，in which hydrogen bond was the most important interaction.Amino acid residues Lys511，His513，Tyr520，Tyr523 in ACE molecule were the most important binding sites combined with active peptides.N-terminal amino groups and C-terminal carboxyl of ACE inhibitory peptides were the key groups for the activities of tripeptides，especially the N-terminal amino groups.The above information will be helpful for the development of ACE inhibitory peptides with high activities.