Abstract: The dynamic performance of assistant gas plays an important role on cutting kerf forming in laser cutting process.The VOF method and depth adaptive laser heat source were used to set up a multiphase flow model which can simulate the interaction between assistant gas and cutting kerf.Cutting experiments were carried out to verify this model.The cut kerf morphology,dynamic performance of assistant gas and temperature distribution were investigated from holing to stable cutting in the total cutting process.The calculation results show that the dynamic performance of assistant gas changes constantly during laser holing,which is affected by cutting frontier shape and cutting depth,etc.Assistant gas flow,cutting kerf morphology and temperature are no longer changing during stable cutting stage.The model can effectively reflect the cutting depth and width which are influenced by dynamic performance of assistant gas.