The invention relates to a device for measuring an extremely-low gas flow based on the static expansion vacuum standard. The device comprises a backing pressure measurement system, a first valve, a gas pressure relief system, a second valve, a calibration chamber, a third valve, a small hole, a fourth valve, a fifth valve, a getter pump, a sixth valve, a molecular pump, a backing pump and an ionization gauge, wherein the backing pressure measurement system is connected with the gas pressure relief system through the first valve, the gas pressure relief system is connected with the calibrationchamber through the second valve, the small hole is connected in parallel with the fourth valve to form a parallel structure and then one end of the parallel structure is connected with the calibration chamber through the third valve and the other end of the parallel structure is connected with a vacuum system, the getter pump is connected with the calibration chamber through the fifth valve, thebacking pump is connected in series with the molecular pump and then connected with the calibration chamber through the sixth valve, and the ionization gauge is directly connected on the calibration chamber. The invention adopts the gas pressure generated by the static expansion vacuum standard to replace the introduced gas pressure of the gas flow meter in the constant conductance method, so as to further improve the gas flow measurement accuracy.