Abstract: Large pumping stations play a key role in irrigation, drainage, water diversion, urban water supply and sewage, which protecting the safety of people's lives and property, promoting economic development, improving people's lives and constructing ecological environment. Especially for step pumping stations, there are lots of the facilities and equipments with large installed capacity , long running time, high energy consumption and operating costs. Pump stations have close hydraulic connections among each step, and the flow and water level are interacted with each other, which restrict the operation of the entire step pumping station system. The optimization scopes for large pumping station operation are gradually expanded. The economic operation of a pump or a pump assembly is progressively developed to a single pump station, the parallel pumping station group and step pumping station system. The factors are considered more and more comprehensively as well. The optimizing goal is gradually developed from high pump efficiency to the highest efficiency of pump assembly and pumping stations. In addition to the energy consumption of the main pump units, it also includes the energy consumption of the auxiliary equipment, trash clean-up equipment, power transmission facilities and transformation system in a pumping station. In the existing research, only the energy loss of main pump unit (including the pump assembly, the drive apparatus and the motor) is taken as the research goal, or even the energy loss of the other device (or facilities) is considered, it is only estimated. So, there is improving space in energy-saving effect. In order to know energy saving effect for large pumping station system, the research scopes of optimal operation schemes for large pumping stations were analyzed. Taking the highest pump assembly efficiency as the optimization objective, optimal models were established for a single pump unit by adjusting pump blade angles and rotational speeds respectively. Also, under the circumstances of certain pumping discharge and pump assembly head, aiming at the lowest operation cost, optimal models were established for a single pumping station and parallel pumping stations. Under the circumstances of pumping certain volume, aiming at the lowest operation cost, optimal models were separately established considering head variation and time-varying electrical price for a single pumping station, parallel pumping stations, parallel pumping station system and step pumping station system. Considering different research scopes and factors, the optimal results of three calculating cases indicate that pump assembly efficiency at optimal blade angles is maximum increased 4.21 percentage points for a single pump unit. Electrical costs of optimal schemes are saved by 5.64% and 6.83% than that of design schemes for a single pumping station system considering time-varying electrical price and blade adjustment and step pumping station system. Energy losses of power transmission and transformation, pumping stations and water transmission should be considered comprehensively when establishing optimal models. The research scopes and factors are more comprehensive, the energy and cost saving effect is more significant. In the optimal models, if the considered scopes and factors are added, the variables will be more, and the solving progress will be complex with heavy calculating load and long calculating time. Therefore, the suitable optimal methods should be further researched aiming at the characteristics of the optimal models for large pumping station system.