To study the flow law in the suction chamber of a centrifugal pump when conveying the gasliquid twophase medium, a transparent model pump was experimentally studied and the gasliquid twophase flow in the pump was numerically simulated based on the EulerianEulerian heterogeneous flow model. The twophase flow in the suction chamber was studied in detail by using the numerical calculation model verified by the experimental results. Thereafter, the variation law of flow patterns in the suction chamber was revealed, and the relationship between the flow pattern and the external characteristics of the pump was established. The results show that, there may be up to eight flow patterns in the suction chamber, while at a certain rotational speed, there will only be six flow patterns at most. The gas spiral length decreases with the increase of the liquid flow rate and increases with the increase of the rotational speed. The appearance of spiral flow greatly increases the turbulence intensity in the suction chamber and reduces the stability of the pump. When the flow pattern in the suction chamber is steady spiral bubble flow, the pump head of pump is relatively large. When the efficiency of centrifugal pump is the highest, the flow pattern in the suction chamber is steady non spiral bubble flow or pulsating non spiral bubble flow.