The toughness of NiCrMoV steel welded joints for nuclear power low-pressure welded rotor is investigated. The impact toughness tests are carried out about the base material,joint heat affected zone,columnar crystal zone in weld,and the fine grain zone in weld. Combining with the fracture morphology and microstructure characteristics,the interrelationship mechanism between resilience and organization is studied. The results show that the impact property of each zone in welded joints can meet the requirement,but the impact property of the heat-affected zone fluctuates greatly. The cracking of the columnar crystal zone along the grain boundary makes the impact property weak. The cracks extend along the columnar grain boundary and a small amount of carbide precipitate on the columnar grain boundary,which is the main reason for the low toughness of the columnar crystal region in the weld.