A new one knob self optimizing fuzzy control system of CO 2 arc welding is established based on the synthetic performance evaluation of droplet transfer process. It includes two kinds of self optimizing fuzzy controllers: the arc voltage controller and the current waveform controller. The fuzzy control principle and the key points of the control patterns are presented. Through on line detecting, computing of characteristic parameters and one knob self optimizing adjusting, the characteristic parameters and welding variables can be adjusted to suitable ranges under the control of the arc voltage controller. Meanwhile the current waveform controller is active in the rear time stage of the short circuiting and the instant of re triggering arc. The experiment results show that the control and its algorithm can improve the synthetic performance of arc welding process apparently. A new one knob self-optimizing fuzzy control system of CO 2 arc welding is established based on the synthetic performance evaluation of droplet transfer process. The fuzzy control: the arc voltage controller and the current waveform controller. principle and the key points of the control patterns are presented. Through on line detecting, computing of characteristic parameters and one knob self optimizing adjusting, the characteristic parameters and welding variables can be adjusted to suitable ranges under the control of the arc voltage controller the current waveform controller is active in the rear time stage of the short circuiting and the instant of re triggering arc. The experiment results show that the control and its algorithm can improve the synthetic performance of arc welding process apparently.