Abstract: The arc-assisted active TIG welding（ AA-TIG） was used to weld 8 mm thick SA537 CL2 low alloy steel and S32168 stainless steel without bevel butt,which realized efficient one-side welding with back. Microstructure and mechanical properties of the joint were analyzed.The results showed that SA537 CL2 heat affected zone produced granular bainite,microstructure of SA537 CL2 fusion zone was interlaced granular bainite and lath martensite. Microstructure of the weld was mainly lath austenitic and residual austenite. Microstructure of S32168 heat affected zone was still austenite,but the grains grew slightly. Hardness of the joint was higher than that of the base metal,and carbon was accumulated at the fusion interface of SA537 CL2 and the weld to form a high hardness carbon-reinforced layer. Tensile fracture was ductile fracture at room temperature in the fusion zone of SA537 CL2 side. Impact value of the weld at-20 ℃ reached the level of SA537 CL2 base material.Surface and back bend inspection of the joint were qualified.