Abstract: When rolling the ultra light-wall pipe，such undesirable cases like incomplete extracting of the mandrel and pipe-mandrel clinging together are frequently happen，which，in serious case，might leads to power outage of the retained gear rack，and in turn，causing the accident of bumping of the said rack towards the rear limit position. The conventional rolling process for the ultra light-wall is analyzed. And as a result it is revealed that the too small gap for mandrel extracting acts as the key for causing insufficient mandrel extracting capability as followed by extracting failure. Accordingly the isometric mandrel is designed and modified，and the cone type mandrel is further developed as well. The said cone type mandrel has been put into actual operation，showing significant effectiveness.