Using internal welding machine for root welding+ automatic solid wire gas shielded vertical down welding for long-distance pipeline welding construction has the advantages of easy process control, high welding efficiency and stabile welding quality. However, due to factors of pairing and beveling,it’s difficult to apply current automatic welding technology in the construction of pipeline tie-in. In order to realize the automatic welding of pipeline tie-in with irregular width and large offset, on the basis of automatic CPP900-W1 single welding torch pipeline welding system, by adopting flux-cored wire gas shielded welding process, the equipment function and welding parameters are optimize through experiments. With the groove pairing offset of 3 mm and pairing gap of 2 mm between the flat position and overhead position welding, the welding equipment and parameters meeting the requirements of automatic welding of tie-in are obtained. Non-destructive testing result and mechanical properties of welds meet the requirements of relevant standards. This welding equipment and process have been applied on the site of East China-Russia gas pipeline and is proved of good application effect. Welder labor intensity is greatly reduced and welding efficiency is highly improved.