Abstract: For the shortage of short circuiting transfer for general CO₂ welding machine, based on the hardware system of digital signal processor and microprocessor control unit, the hierarchical in-telligent control theory was applied and the hierarchicall intelligent full digital control schematic for CO₂ short circuiting transfer welding was put forward. It integrates the digital PI controller, fuzzy con-troller and expert system, which make control levels clearer and design scheme easier. The experimental results validate that this sy stem can attain ideal waveform control for CO 2 short-circuit welding, and improve CO₂ welding machine performance, and control welding process intelligently.