The invention relates to an all-plastic diaphragm-type one-way air-exhaust check valve with the emergency ventilation function. The all-plastic diaphragm-type one-way air-exhaust check valve comprisesa valve body, a first valve plate mounting cavity and an air purifying assembly mounting cavity are arranged in the valve body, an outer clamping buckling fastening piece is arranged on the side faceof the valve body, an air exhaust opening is formed in the outer clamping buckling fastening piece, a first valve plate is mounted in the first valve plate mounting cavity, a supporting piece is arranged at the lower portion of the first valve plate, a plurality of hollow parts and supporting reinforcing parts are arranged on the supporting piece, an air exhaust crack is formed in the first valveplate, the air exhaust crack divides the first valve plate into a plurality of air exhaust valve clacks, a dome part is arranged on the position, located at the upper portion of the first valve platemounting cavity, of the side face of the valve body, and a supporting piece damaging column is fixed on the inner wall of the dome part. Under the emergency state of losing the air source of the valve, the one-way non-return function of the first valve plate can be quickly transformed through hard pressing of the dome part of the valve body, meanwhile, a second valve plate sealing structure can be quickly destroyed manually, the two-way flow of the air flow is achieved accordingly, and the breathing need of a wearer under the emergency state is met.