Abstract: Welding and postweld heat-treatment were carried out for low-temperature steel 07MnNiCrMoVDR.Low-temperature impact toughness was tested, the fiber percentage of fracture at different temperature was calculated, macroscopic and microscopic fracture and microstructure were analyzed for base metal, weld seam and heat-affected zone.The results indicate that impact energy of every zone meets requirement of 07MnNiCrMoVDR steel's mechanical property.It also shows that the chosen welding technology and postweld heat-treatment technology are reasonable.Fiber percentage in base metal fracture is higher than that in heat-affected zone fracture and it is the lowest in welded seam fracture through calculation of fracture's fiber percentage.It indicates low-temperature impact toughness of base metal is the highest, and its is higher in heat-affected zone than that in welded seam.