Abstract: A single-chip microcomputer-controlled SMAW (shielded metal arc welding) welder trainer is developed. It is a type of mechatronics simulator for welder training. By using this equipment, welder training for elementary SMAW operation technigue can be accomplished without welding equipment, electrode or steel workpiece. It can simulate the melting process of electrode and the travelling of the molten pool, detect and determine the position and the inclination of the simulated electrode, judge whether the operation of the trainee is in accordance with the standards. The simulated arc sound and alarm signal are fed back to the traince for real-time controlling, and the number of times of operating fault is recorded simullaneously. In this paper the system structure, working principle and computer program arc introduced.