Abstract: In order to carry out fast, effective, safe, low cost fire preventing and extinguishing with liquid nitrogen, we design the mobile fire-fighting device with liquid nitrogen for coal mine. The main structure of the device is composed of three parts, which are liquid nitrogen storage, liquid nitrogen output control part, and mobile carrier. According to the strain hardening method, the design calculation and strength check of the liquid nitrogen storage tank are carried out. The closed loop control system of liquid nitrogen output is composed of cryogenic electric proportional control valve, cryogenic differential pressure liquid level meter, cryogenic liquid nitrogen flow meter and PLC control box, which can adjust the output volume of liquid nitrogen, automatic exchange to ensure the injection of liquid nitrogen column. The mobile carrier adopts the structure of the coal mine flat car, and the special improvement is carried out.