In order to explore the simulation and calculation of a water hammer with liquid column separation, a new cavity model was proposed based on the improvement of a discrete vapor cavity model (DVCM). The non-full flow pattern in the cavity was considered in the new cavity model, and according to the flow state of the upstream and downstream sections, the calculated sections were divided into seven types. Calculation modules were established to calculate the classified cavity sections and the transient process of the cavity was simulated more accurately.The new model was preliminarily verified by simple pipeline and complex pipeline tests. The results show that compared with the traditional DVCM, the new cavity model can more accurately predict the pressure fluctuation, cavity shape, location and volume change in the transient flow.The simulation of the peak pressure fluctuation in the process of water column bridging is closer to the measured data, which helps to guide the safety protection of water hammer in engineering.