Abstract: Because of the large head variation range in one water control project,it is difficult to fully meet the performance requirements of the pump turbine unit,and this problem needs to be solved by means of variable speed. By using frequency conversion and speed regulation technology,for the first time,the pump turbine unit can not only pump water with frequency conversion,but also generate electricity with frequency conversion,thus solving the technical problems of large range of head variation both under pumping condition and under power generation condition. The research method can improve the guarantee rate of water supply and the economic benefit of power generation.