The invention discloses a method and a device for measuring adsorbing capacity of a molecular sieve on the basis of gas consumption. The gas volume variation after the gas is adsorbed by the molecular sieve is utilized to measure the adsorbing capacity of the molecular sieve for the gas. The device comprises a gas storage tank, an adsorbing tank, a gas source, a vacuum pump, a gas flow meter, a gas stop valve, a gas pipe, a vacuum display unit, a gas pressure display control unit, a molecular sieve bed, a metal heating wire, a temperature sensor, a temperature display controller and the molecular sieve. Before the test, the vacuum pump is used for vacuumizing the gas storage tank and the adsorbing tank; the gas passes by the gas flow meter and reaches the gas storage tank and the adsorbing tank; after the adsorption reaches a balanced state, the gas remained in the gas storage tank and the adsorbing tank is subtracted from the gas flow recorded by the gas flow meter, so that the adsorbing capacity of the molecular sieve can be measured. The method and the device can be utilized to measure the adsorbing capacity of a zeolite 3A molecular sieve for HF gas under the room temperature and different pressures. The operation is simple and convenient.