In order to study the flow characteristics of centrifugal pumps when transporting the gas—liquid mixture, water and air were chosen as the working medium, numerical simulation was conducted on a centrifugal pump under different conditions of inlet gas volume fraction （IGVF） based on the Eulerian—Eulerian inhomogeneous model. The drag force was approximated by the Schiller Nauman model. No other interfacial forces were considered. The gas distribution and velocity streamline in the impeller were obtained to discuss the gas and water flow characteristics of the pump. The results showed that gas concentration was high at the inlet pressure side of the blade, where the vortex would exist, indicating that the gas concentration had a great relationship with the vortex aggregation in the impeller passages. When the IGVF was increased to 10%, phase separation had obviously appeared at the suction side of the blades in the impeller passages, and gas had a movement trend along the suction side to the outlet of the impeller. Gas was moved from the center of the passages to the front and back shroud, and with IGVF increased, gas fraction in the back shroud near the leading edge and back shroud would be increase. Gas fraction in the front shroud near the trading edge was increased significantly than that in the back shroud, and the gas may eventually choke the passages. Within a rotation period, the outlet pressure of impeller was cyclically changed, when IGVF was increased from 1% to 10%, the outlet pressure of impeller was gradually decreased, and pressure pulsation frequency of the monitors was near the blade passing frequency at different IGVF values. When the IGVF was not higher than 10%, IGVF had no obvious effects on the pressure pulsation frequency and time frequency of the monitoring points. By comparing the experimental results with the numerical results, the reliability of the mathematical model and calculation methods was confirmed.