A　fully　digital　wire　extension　fuzzy　control　system　for　CO2　short-circuit　welding　is　presented.　The　main　component　is　a　digital　signal　processor　ASDP2181　of　ADI　company,　and　the　digital　fuzzy　control　system　also　is　designed　and　embedded　in　digital　signal　processor.　It　includes　the　fuzzy　controller　module　which　is　designed　to　modulate　wire　speed　and　the　waveform　parameters　modulation　module　which　is　used　to　modulate　waveform　parameters　for　short　circuit　CO2　welding　and　output　voltage　of　welding　machine.　The　welding　process　experiment　proves　that　this　system　can　keep　arc　stability　and　weld　appearance　in　spite　of　the　change　of　wire　extension　by　measuring　and　calculating　the　average　welding　current　online　and　automatically　adjusting　wire　speed　and　waveform　control　parameters.　The　change　of　wire　extension　can　be　compensated　in　8-45　mm.