Abstract: The toughness of weld joint with deposit metal yield strength exceeding 785MPa after different stress relief heat treatment was investigated.The result indicated that the cooling rate was critical factor to toughness of weld joint subjected to stress relief heat treatment.The structure analysis indicated that segregation on grain boundary of weld joint subjected to stress relief heat treatment was main phosphorus.There was small reverted austenite in lath-shaped martensite in the weld joint which was of benefit to improving toughness of weld joint.