The invention provides a check valve for controlling air current to flow in one direction on an engine, which consists of an upper shell, a lower shell, a membrane and a support sheet. The support sheet and the membrane are matched with a positioning boss of the upper shell through a mounting hole and are matched with a positioning hole of the lower shell to realize axial limitation of the membrane through the positioning boss of the upper shell. Gas acts upon the membrane from an air inlet of the upper shell to an air pore on the support sheet, the membrane carries out structure deformation under the action of the air current to reserve a gap with the upper shell, and the air current passes through an air outlet of the lower shell to flow out through the gap to realize the flowing actionof positive air current of the check valve. When the gas flows reversely, the membrane cannot deform due to the action of the air current, the reversed air current is stopped by the matched sealing action of the membrane and the upper shell, and the membrane has favorable sealing performance on the reversed air current. The check valve has the advantages of simple structure composition, easy assembly, light weight and small volume, can ensure that the air current is smooth when the air current positively flows, and has favorable airtightness when the air current reversely flows, thereby the requirements on related performance are satisfied.