<p>During strong unsteady flow processes such as cavitation initiation and collapse, the volume changes generated by the materials transformation of cavitation phase transition seriously lag behind the volume evolution formed by the flow process. The phase transition and hydrodynamics are in a non-equilibrium state. A cavitation model that can describe such non-equilibrium phenomena is needed in numerical simulations of cavitation flow. The paper starts from the molecular dynamics’ principle of phase change of matter, and based on the Maxwell velocity distribution form of molecular thermal motion, elaborates on the formation process of Hertz Knudsen formula for material exchange at the interface between liquid and vapor. On this basis, using the evolution equation of gas nucleus number density in water and the compressible state equation of vapor, a non-equilibrium cavitation model for phase transition and hydrodynamics is established. The simulation results of a vapor bubble collapse process in the non-equilibrium cavitation model show different behavior from the simulation results of the equilibrium cavitation model. The simulation results of the equilibrium cavitation model show that the vapor bubble collapses once and completely disappear, while the simulation results of the non-equilibrium cavitation model show multiple collapses and rebound, which is agreement with the experimental results of the vapor bubble collapse.</p>