The utility model relates to a gas pressure reducer for mass flow. The gas pressure reducer for the mass flow mainly comprises a pressure reducer valve body, a valve body cover, a valve core, a gas membrane assembly, a regulating assembly, a pressure regulating assembly, a connecting assembly, a pressure gauge and the like. According to the gas pressure reducer for the mass flow, the pressure of a regulating spring is changed by regulating rotation of a screw rod, so that the size of an opening clearance of a regulating mechanism is driven to change, the pressure at an inlet position is reduced and regulated to a needed outlet pressure value, the aperture of the valve core is controlled through a feedback action of the outlet pressure, and the stability of the outlet pressure is maintained. The movement of the regulating mechanism is directly related to the outlet pressure, once the outlet pressure is changed, the valve core can move with the outlet pressure to achieve a function of stabilizing the pressure of the pressure reducer. The gas pressure reducer for the mass flow has the advantages of being simple in structure, accurate in regulation, long in service life, small in size and capable of guaranteeing output of mass flow gas. Working condition requirements of special working conditions for small size, large output pressure and mass flow are completely met.