The development of low temperature steel at home and abroad and the safety problems in its application are introduced. The difference between ductile fracture and brittle fracture,ductile and brittle transition and brittle fracture mechanism at low temperature are described. The key technologies for evaluating low temperature toughness of low temperature steel are reviewed from the aspects of process,micro-structure,mechanical method,EBSD analysis technology and small punch test. The problems needing attention in low temperature steel welding are also described. Finally,the future development trend of low temperature steel is prospected.