The invention discloses a load self-adaptation gas-fired device of a gas engine. The load self-adaptation gas-fired device of the gas engine comprises an air channel, an air inlet, a gas channel, a gas inlet, a mixed gas channel, a mixed gas outlet, an upper diaphragm assembly, a lower diaphragm assembly, a gas chamber, a mixed gas chamber and an air chamber, wherein the gas chamber and the mixed gas chamber are separated by the upper diaphragm assembly, the air chamber and the mixed gas chamber are separated by the lower diaphragm assembly, the upper diaphragm assembly and a lower piston are fixedly connected into a whole through an adjusting threaded rod, the lower diaphragm assembly and an upper piston are fixedly connected into a whole through a pressure plate, metering holes are formed in a piston sleeve, and are used for input of air and gas and output of mixed gas, the metering holes are in a plugged or an open state along with movement of a piston head, and the upper diaphragm assembly and the lower diaphragm assembly can move vertically along with changes of air pressure, and drive the upper piston and the lower piston to move perpendicularly, so that the size of the air metering hole and the size of the gas metering hole are changed. The load self-adaptation gas-fired device of the gas engine can automatically provide the mixed gas with the appropriate amount according to the requirement of the gas engine, and can also automatically adjust the concentration of the mixed gas according to the requirement of load changes so that the purpose of improving power performance of the gas engine and the purpose of saving energy can be achieved.