Abstract: The demand for clean energy in China will be further increased during the ‘14th Five-Year Plan’ period.Liquefied natural gas (LNG) is an important part of the national energy strategy. LNG storage tanks are one of the major infrastructures，and the welding technology of storage tank is the key to ensure the safety and service life of facilities. In this paper, the new TIP-TIG automatic welding technology was used to weld the inner tank of storage tank. The microstructure, mechanical properties and low-temperature impact toughness of TT welding and SMAW welded joints were compared and studied by means of electron microscopy, energy spectrum analysis and X-ray diffraction. The results show that the TT welded joint has the advantages of high strength and low temperature toughness, which is mainly due to the small heat input of TT welding, stable welding process and small fluctuation of welding process parameters, resulting in good forming of welded joint and small fusion ratio. The microstructure of joint is mainly austenite with fine grains, and the element desolventizing precipitation is less. The precipitated phase is Mo-rich phase with high Mo content, which hinders dislocation slip, and has a some precipitation strengthening effect. Less precipitates avoid the formation of hole nucleation caused by gravitational concentration caused by inclusions and improve the toughness of the joint. With the improvement of automation, this welding method can replace SMAW and become a new welding technology for vertical seam of LNG storage tank.Highlights: In this paper, the mechanical properties of TT and SMAW welded joints were compared and studied for the first time. TT welding has the characteristics of small heat input, stable welding process, good joint forming, small fusion ratio and fine weld grain, which makes TT welding joint have the advantages of high strength and good low-temperature toughness. It can replace SMAW and become a new vertical welding technology of LNG storage tank.Key words: 9%Ni steel, TIP-TIG welding, SMAW, microstructure, low temperature toughness