Abstract: Taking No.4 Jiangdu Pumping Station as a study case, which is one of the source stations in Eastern Route of South-to-North Water Diversion Project in China, the optimal operation of single pumping station for multiple pump units with variable speed was studied. The non-linear model of optimal daily operation for multiple pump units with variable speed was constructed with consideration of peak-valley electricity price and tides variation. Keeping the blade angle of pump unit at designed value, this model took the minimal electricity cost of multiple pump units as objective function, the time period as stage variable, the pump speed and quantity of operation units as decision variables, and the quantity of daily water pumped as constrain condition. The method which took the pump speed for experimental optimization, the quantity of operation units for linear integer programming was proposed to solve the model. The optimization results showed that under the average daily head of 7.8-3.8m, considering peak-valley electricity price and with 100% loads, the cost saving of water pumping per unit was -3.58%~-2.14% compared with operation in rating state, which showed that the optimization effect could not counteract the energy loss carried out by frequency converter. While under 80% and 60% loads, the optimization effect was obvious and the cost saving was 11.38%-15.71% and 24.79%-29.17% respectively. Under the average daily head of 7.8~3.8m, without considering peak-valley electricity price, the optimal operation had some benefits only under the low heads and with small operation loads(such as 5.8 m and 60% loads；4.8 m and 80% loads; 3.8 m and 60% loads). While under the other heads and loads, the optimization effect could not counteract the energy loss carried out by frequency converter. The results can provide a new way for optimal operation of large-scale pumping station influenced by tides for multiple pump units with variable speed.