The construction of liquefied natural gas（LNG）storage tanks is complicated and the technical requirements are very strict. Currently,9Ni steel is commonly used in the manufacturing of LNG storage tanks. 9Ni steel is a low-carbon martensitic ultra-low temperature steel with a Ni content of 9%.It has excellent strength and toughness at -196 ℃. The welding materials and welding technology of 9Ni steel are difficult and key points in the construction of LNG low temperature storage tanks. A few developed countries in the world have been mastering these technologies. The localization of 9Ni steel welding has become the focus of the industry. Based on the research on 9Ni steel and its welding materials in recent years,this paper summarizes the development and technical chara-cteristics of 9Ni steel,and discusses the development of its welding materials,welding methods and welding processes.