By using a front-tracking method

the dynamic characteristics of the droplet impact onto liquid film were numerically simulated. Through analysis of the liquid topology evolution and internal physical field information obtained after impacts

the influence of We number and dimensionless liquid film thickness on interface motion was studied

and the mechanism of air entrainment phenomenon in the impact process was expounded. Further researches show that small jets occur in the neck region after impacts

which is the basis of the formation of the crown. In the horizontal direction

the pressure does not change in the area where the impact does not affect

while there is a local pressure difference near the neck of the small jets. During the droplet liquid film impingement

the gas layer is compressed

and under the joint action of fluid viscosity and shearing force

the gas escape velocity in the gas layer with high pressure is slowed down to form a air entrainment phenomenon.