Bi-metal composite pipe and corrosion-resistant alloy prefabricated inner-filled steel pipe have been widely used in oilfields due to their excellent corrosion resistance and performance-free joint characteristics. Especially the corrosionresistant alloy prefabricated inner-filled steel pipe is relatively inexpensive. In recent years,the cost has been promoted in a large area of high-corrosion ground pipelines in domestic oil fields,and has achieved very good results. Due to the differences in the chemical composition,microstructure,and physical properties of the inner and outer layers of the bimetal composite pipe, the commonly used butt welding process has the problems of complex procedures,difficult operation,high construction costs,and strict requirements for welder skills,which can easily cause composition segregation,dilution of corrosion-resistant alloy components,poor internal bead forming,false welding,carbon migration,and structural changes in the fusion zone caused by heat input. This article starts from the factors that affect the quality of bimetal welds,and takes the horizontal fixed butt welding of stainless steel composite pipes as the research object.Research and experiments have been carried out from the bevel form, the pairing method,the welding method of the corrosion-resistant alloy underlayer and the bimetal transition welding layer,and new process methods such as internal sealing of composite pipes,U-shaped groove free-space group pairing,back protection of the molten pool,unfilled fusion welding bottoming and unfilled fusion welding transition have been proposed.Through X-ray inspection and welding process evaluation,combined with microstructure analysis,comprehensively evalu-ated the welding process and concluded.