Abstract: The GDC（He） is an effective method for controlling wall H recycle and C, O impurities and improving the vacuum wall conditions in HL-1M tokamak.It is characterized of simplicity, no magnet and safety comparing with TDC,AC and ECR. Comparing with degassing bake-out,it has the higher degassing rate during GDC（He）and lower impurity concentration in vacuum chambers after GDC（He）.The cleaning patterns of dominant de-oxygen,de-carbon and de-hydrogen are introduced and the cleaning parameters for wall H recycle and wall cleanness are suggested.