At present, few scholars have studied the new surge well that combining water chamber with overflow, which can effectively reduce the height of surge well by overflow weir and water chamber. Therefore, it is necessary to conduct more studies on this type of new surge well. Hydraulic calculation of the new surge wells is an important subject due to the complex calulations. Taking the new surge tank of Lazhai Hydropower Station as an example, this paper establishes a mathematical model through the diversion system of the hydropower station. The influence of non-linear factors in each link of the system is fully considered. The boundary conditions of upstream reservoirs, bifurcated pipelines, surge wells and hydraulic turbines are also taken into account. The pipeline water hammer calculation is carried out by the method of collecting lines. The Toma formula is used to calculate the stable section of surge shaft. The results showed that when the unit load suddenly changes, the unit speed changes accordingly, the fluctuation of surge well water level decreases continuously, and the final water level is stable. In addition, the speed, volute and draft tube pressure of the unit meet the requirements of specifications and reach the economic and safe and reliable range. The maximum adjustment deviation of the unit is small, the time is short, the number of oscillations is small, and the dynamic quality index is good. The lowest surge water level of surge wells is higher than the bottom elevation of surge wells, and the highest surge water level of surge wells is lower than the top elevation of surge wells, which meets the requirements of no aeration and overtopping of surge wells. Therefore, the shape design of the new surge wells is reasonable and the hydropower station operates safely.