A drainage system includes at least one inflow pipe, a first outflow pipe, and a pressure vessel connected to the inflow pipe and the first outflow pipe separately. A throttle orifice plate and at least one switching valve are connected in series on each inflow pipe, and a throttle orifice plate and at least one switching valve are connected in series on the outflow pipe. The drainage system further includes a pressure release device, a check valve is also connected in series on each said inflow pipe, and a pressure measurement device is also connected to the pressure vessel. The pressure release device is an automatic pressure control valve connected to the pressure vessel. The drainage system for a gas turbine can remove condensate during operation of the gas turbine, thereby ensuring safe operation.