In order to study the influences of the location and area of the tailrace surge chamber on the draft tube pressure, with the common hydropower transition process software, a model was established and used for numerical calculation and analysis,combined with an engineering example of restricted orifice tailrace surge chamber. The process considered the hydro-turbine characteristics，the boundary conditions, the closing law of guide vane and the effects of elastic water hammer. The results showed that, it was not true thatthe closer the distance between tailrace surge chamber and hydropower house, the more beneficial to the pressure value of the draft tube. There was a critical position of the draft tube minimum pressure value, the changes of surge chamber area also greatly affected the minimum pressure value of draft tube .When the tailrace surge chamber exceeded the critical position and moved towards the direction of the hydropower house, the change in the minimum pressure of draft tube was small, which did not improve the minimum pressure of the draft tube significantly. However，when the area of surge chamber increased, it obviously changed the minimum pressure in draft tube. This conclusion is beneficial to the arrangements of the surge chamber and underground hydropower house, and it also alleviates the contradiction between the stability of surrounding rocks and the safety in hydraulic transition process.