Hydraulic interference occurs in a power plant with one pipe and multiple machines, which is a special transition process between large fluctuation and small fluctuation. In order to study the influence of the parameters of surge tank on the regulating quality of the unit under the condition of hydraulic interference, two typical hydraulic interference conditions are selected, and numerical calculation and analysis are carried out for different combinations of parameters of surge tank and two different regulating modes. The results show that the area of impedance hole has a great influence on the regulating quality of the unit under the condition of hydraulic interference. When d=2.7 m is selected, the unit can be operated normally. When the maximum output swing of the unit is small, it can also regain the stable state in a short time. When the large well area of the surge chamber is large, the disturbed unit can regain the stable operation state in a short time. The flow coefficient of the impedance hole has little influence on the regulating quality of the normal unit under the hydraulic interference condition.