Abstract: The Jiuxi Drainage Pumping Station in Hangzhou City, Zhejiang Province is equipped with six large mixed flow pumps with guide vane, with a single unit flow rate of 50m3/s and a single motor power of 10 000 kW. It is the largest mixed flow pump with vane diffuser in China. Affected by the upstream inflow and downstream Qiantang River tide, the pump head has wide range of variation. The minimum head is 1.71 m, the design head is 14.0 m, and the maximum head is 15.4 m. In order to ensure that the pump unit maintains safe and stable operation within a large range of head changes, combined with the building layout and operation conditions of the Jiuxi pumping station,the downstream tidal gates were fully utilized to increase the minimum head, and the effects of full regulation and variable frequency regulation on optimizing low head operating conditions were analyzed and compared in detail, and comprehensive measures to improve the stiffness and strength of the pump unit were adopted. A detailed analysis of the pump unit operating conditions and selection scheme is conducted, and suggestions for frequency conversion adjustment and operation optimization of the pump unit are proposed, providing reference for similar pumping stations.