As the key technology of magnesium alloy application, a set of double-chamber gas protection system has been designed ground on process expert database. In view of the different needs of flux and concentration for the cover gas under different furnace system states, this PLC control system based on the process expert database meets the requirements of gas protection control system effectively. The automatic judgment of furnace system states and intelligent adjustment of control parameters have been achieved by control system. And the double-chamber gas protection control system can carry out the independent control of cover gas led into melting room and holding room. Then the flux and mixing ratio of cover gas can be precisely controlled to meet the requirements of effective protection when the magnesium alloy melting system under different states. At the same time, the effect of gas protection can be obtained through using the minimum dosage of cover gas, and the negative effects on the environment can be decreased extremely. Simulation was conducted based on the characteristics of continuity of temperature change, which was shown that in different conditions this control system could obtain the requirements of cover gas control flexibly and effectively, which are set by the process expert database.