The invention provides a vacuum metering device and belongs to the technical field of gas metering. The vacuum metering device comprises a desorbing device, a metering device and a sampling bottle, the desorbing device comprises a reaction tank used for containing a sample and a heating device used for heating the reaction tank, the metering device comprises a first metering barrel, a first transition barrel, a second metering barrel, a second transition barrel, an air pump and a vacuum pump which are communicated with one another through a pipeline, multiple pneumatic valves are arranged on the pipeline, the first metering barrel is communicated with the reaction tank, and the second metering barrel is communicated with the sampling bottle. The vacuum metering device is of a double-metering-barrel structure, thereby being capable of measuring gas large in size in one step, and is simple and convenient to operate, few in measuring error and more accurate in result.