Aiming at the problem of wire extension stability in aluminum alloy pulsed MIG welding process, the influence of wire feed speed on wire extension is identified and the mathematic model has been set by the step response experimentation. According to the actuality problem of routine PID control, a self-tuning fuzzy PID system in a dynamic process was designed to improve the adaptability and the control accuracy,and system simulation was conducted by using the Simulink toolbox of MATLAB, and the optimum control parameters was obtained, then the real-time control for wire extension was carried out based on xPC target real-time environment. The results show that the obtained identification model can reflect the change law of wire extension well and the designed self-tuning fuzzy PID system can control the wire extension effectively in aluminum alloy pulsed MIG welding and also have fast response and good robustness.