Abstract: For Q235B+304 thin lined composite pipe with a 0.6 mm+4.0 mm cladding that could not be welded alone, three-pass welding method of transition layer + two cover layers and tungsten argon arc welding (TIG) were adopted respectively. Commonly used ER309L welding wire, ERNiCrMo-3nickel-based alloy welding wire and TGF309L welding wire with coating were used for transition layer welding respectively, ER70S-6 welding wire was used for cover welding, and three kinds of welding schemes were designed. Microstructure analysis, tensile and hardness tests were carried out on welded joints, focusing on analysis of weld performance of transition layer to verify feasibility of thin-lined composite pipe welded by the three-pass welding method of transition layer + two layers of cover layer, and properties of welded joints of three transition layer welding consumables were compared. The results showed that welds under three welding schemes were well formed, and three transition layer welding materials and composite pipe had good weldability. Transition layer weld with ER309L and TGF309L welding wires consisted of austenite and a small amount of vermicular ferrite microstructure, transition layer weld with ERNiCrMo-3 welding wire was composed of fine nickel-rich austenite equiaxed grains and intergranular microstructure, and cover layer weld with ER70S-6 welding wire was made up of lath-like martensite microstructure. Tensile strength of three groups of welded joints all met basic requirements of base metal of composite pipes. Local hardness of nearby fusion line between base metal and transition layer weld increased due to carbon migration which was weak link of welded joints.