Applying the single chip microprocessor in the process of controlling gasproportion mixing has several advantages such as good systematic stability, high precision,flexibility to supply different amount of gas, and being used in the practical productionprocess of modified atmosphere packaging. This introduced control1ing principle, hardwarestructure and precision of the equipment that is newly developed GM - A, GM - B gasproportion mixer's system with the single chip microprocessor, which realizes the anystipulated two or three gases' volume percentage, controlling all gases' magnetic valves,fulfilling the purpose of obtaining prestipulated proportional mixed gas.