The invention discloses a device for measuring volume flow rate of gas. The device comprises a pressure sensor, an injection pump and a micro processor, wherein the measuring gas passes through a gas pipeline, and acts on the pressure sensor on the one hand, and is connected with the injection pump; the pressure and the initial pressure of the measuring gas are compared by the pressure sensor so as to generate differential pressure signal, and the differential pressure signal is outputted to the micro processor; according to the differential pressure signal, the micro processor generates corresponding control signal to drive the injection pump to pump gas at a corresponding speed until the differential pressure is zero; in the process, the injection pump sends the displacement code signalgenerated during pumping to the micro processor, and the flow rate of the measuring gas is worked out by the micro processor according to the displacement code and the volume of an injector and the pumping time of the injection pump. The measuring device has the advantages of high sensitivity, wide flow rate measuring range and high reliability, and can particularly measure the volume flow rate of the gas with micro flow rate.