Abstract: In this paper, the concept design of tank's breather valve is posed, and the design concept on control object, primary design considerations, on/off behavior and function extension of breather valve are discussed. It is pointed out that the design of breather valve should really start from the vapor tight operation of tank and be based on the maximum air flowrate producing from the breathing of tank, improve the on/off behavior of breathing valve, and has a in-line monitoring function, which is a new design train of thought of tank's breather valve.