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　intelligent　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　controller　and　expert　system,　which　make　control　levels　clearer　and　design　scheme　easier.　The　experimental　results　validate　that　this　system　can　attain　ideal　waveform　control　for　CO2　short-circuit　welding,　and　improve　CO2　welding　machine　performance,　and　control　welding　process　intelligently.