Abstract: Liquid ring pump is a kind of basic equipment that is widely used in engineering fields, such as oil and gas storage and transportation. However, it is faced with the problems of complex gas-liquid two-phase flow, higher energy consumption and lower efficiency, and its performance prediction is scarcely studied. In this paper, therefore, the Eulerian multiphase flow analysis method was used to simulate and calculate the transient gas-liquid two-phase flow in a singlestage double-acting liquid ring vacuum pump. The velocity, pressure and phase distribution of gas-liquid two-phase flow in the liquid ring pump at operating conditions were obtained, and the unsteady characteristics of performance parameters of liquid ring pump (e.g. gas suction flow rates and gas discharge flow rates) and the distribution laws of vortex inside the vane wheel were also figured out. Based on the numerical simulation of flow field, the performance curves of liquid ring pump in different rotation speeds, such as the relationship of gas suction flow rate and shaft power vs. suction pressure, were predicted and verified by tests. It is indicated that the numerical simulation and performance prediction method adopted in this paper can be used as the guidance for the optimization design and application of liquid ring pumps.