As an excellent material, Magnesium (Mg) alloy was widely used in automobile, IT product and aerospace industries. The magnesium alloy heater needs a robust controller to advance on the high accuracy, the static and dynamic stable characters, and the heater’s time delay. Firstly the magnesium alloy furnace mechanical model based on multi-layer equivalent thermal network for a radiant tube is introduced. The numeric model in one dimension steady heat transfer was developed. And a series of linear systemic characters were developed via experimental research. Secondly the furnace control system model was developed, which was built on the PID and Smith predictor in detail. And its kernel algorithm was simulated and applied in the furnace equipment system. Comparison of the Smith predictor and the conventional PID controller demonstrated that the former could eliminate the static error, reduce overshoot, shorten regulating time, and improve control precision and running stability. Finally an example which was a whole process experiment of the Mg alloy melting was given. It should be drawn that Smith predictor control system was superior to the conventional PID controller in the heater.