Abstract: Objective The aim is to meet the welding engineering requirements of inner tank wall plate of big liquefied natural gas storage tank, the effect of different welding methods on the welding process and weldability of 9% Ni steel are studied. Methods This paper studies microstructure, microhardness, tensile strength, low-temperature impact absorbed energy and so on, to compare and analyze the difference of microstructure and mechanical properties of the three welding methods of SMAW, TIG and SAW on the thickest plate, medium plate and thinnest plate of the inner tank wall plate. The effect of welding method and wall plate thickness on weldability is described in detail, the welding stability and difference of 9% Ni steel welding parts are indicated when there is a combined welding behavior on the storage tank construction scene. Resuls The results show that there are differences in the bevel form, welding parameters and weld appearance molding applicable to the three welding methods. The microstructure of the weld zone is all the austenite and the precipitation phase. And then, the microhardness of the weld zone is lower than that of heat affected zone and base material, and the tensile strength decreases with the increase of plate thickness. The comprehensive low temperature toughness from high to low is tunsten inert gas welding, submerged arc welding, shielded metal arc welding. Conclusion The research results of this paper provides certain theoretical support for the selection of inner tank wall plate welding methods and the formulation of welding parameters in liquefied natural gas low-temperature storage tanks.