Because the flow regime of mixed type surge shaft was complicated, The conventional analytical method and graphical methods cannot accurately calculate tits water level fluctuation, pressure difference changes, regulation guarantee change, etc. A numerical simulation of hydraulic characteristics of the mixed type surge shaft was conducted based on the mathematical model , the reliability of numerical simulation results were test by model test, and the feasibility of mixed type surge shaft was discussed. The results showed that, the numerical simulation agreed with model test results basically, and the numerical simulation results were feasible. The highest surge water level was below the top elevation of surge shaft, the lowest surge water level was higher than the required minimum submergence depth, bottom upward surge shaft by the maximum pressure difference was relatively small, the fluctuation of water level moved through the up and down reciprocating, the fluctuation decreased gradually, and finally stabilized. The turbine speed, the spiral case and the draft tube pressure were in reasonable ranges, therefore, the design of surge shaft bottom elevation and top elevation, size of stable impedance orifice and stabilized sectionwas reasonable.