The invention discloses a self-feeding channel-opened / closed positive pressure air respirator comprising a compressed air bottle, an all-face mask, a safety valve, a pressure-reducing valve, an air distributor, a ration air supply valve, an inhalation control valve, an exhalation control valve, an exhalation gas-guide tube, an inhalation gas-guide tube, an external connection rapid port, a clean pot, a Venturi tube valve, a cooling box, a gas temporary storage box, a purge valve, a triple valve, an air gauge, an alarm, a shoulder-hanged display gauge and an intelligent sound box. A fireman can safely use the self-feeding channel-opened / closed positive pressure air respirator for a long time. According to the self-feeding channel-opened / closed positive pressure air respirator, compressed air is used as a main air source, the service time of the limit compressed air can be prolonged in practical applications through cooperation with a carbon dioxide purifying and conversion device and a cooling system device, wherein the cooling system device is used for controlling the direction of air flow and branching the air flow. When a fireman rescue people in the scene of a fire, he can use the self-feeding channel-opened / closed positive pressure air respirator to protect himself in a danger, poisonous, high temperature and anoxic environment for enough time to rescue people or do other special tasks.