Abstract: To study the flow characteristics caused by unsteady gas-liquid two-phase flow in a centrifugal pump with the vane diffuser, the three-dimensional simulation was performed for the gas-liquid two-phase turbulent flow in a centrifugal pump with radial diffuser by the DDES (Delayed, Detached-Eddy, Simulation) model and mixture multiphase flow model. The pressure distribution in impeller and the guide, streamline distribution and pressure fluctuations of monitoring points on volute wall were obtained under different gas volume fractions.We compared the numerical simulation with experimental performance curves with gas volume fraction C_v =0.05.The results show that the gas accumulation is mainly in the leaves near the outlet of guide, and the gas phase in volute is mainly concentrated in the area near impeller side and it is gathered near the tongue in cross section of the volute outlet. Pressure of guide vane outlet decreases in the clockwise direction from the tongue in water and the air liquid two phase flow. The recirculation zone occurs in guide vane near the tongue and the area from the volute tongue to the inner section of the first section and the inside of the section. The static pressure of the volute wall decreases gradually from the P₁ point along the clockwise direction to the volute exit. As the gas volume fraction increases, the lift and efficiency of the model pump are gradually decreases, and the area of low pressure in impeller inlet increases, and pressure in guide vane reduces, and recirculation zone is gathered by multiple small plane for several large recirculation zones on inside of volute outlet section, and static pressure of the same monitoring point decreases, and the pressure value of tongue is affected by gas content largely.