The embodiment of the invention discloses an exhaust system which comprises a gas storage tank, a gas flow speed sensor, a controller and a motor. The gas storage tank is used for storing compressed gas and outputting the gas when a valve of the gas storage tank is opened. The gas flow speed sensor is arranged on the valve of the gas storage tank and used for obtaining flow speed information of the output gas when the valve is opened. The controller is connected with the gas flow speed sensor and the motor, and used for sending out a corresponding control instruction to the motor according to the flow speed information obtained by the gas flow speed sensor. The motor is connected with the controller and used for controlling a piston plugged at one end of space of an inner cavity of the gas storage tank according to the control instruction of the controller so that the space of the inner cavity of the gas storage tank can be changed. Correspondingly, the embodiment of the invention further discloses a method for outputting the gas in a constant flow mode. By the adoption of the exhaust system and the method, the gas of constant flow can be output, and the stability of acting on the outside by the gas can be ensured.