Abstract: To test the weld cold crack sensitivity of Cu-age-hardening steel in humid ambience,two kinds of specimens with oblique Y-groove and straight Y-groove,respectively,were welded using gas metal arc welding.Weld delayed crack experiment of Cu-age-hardening steel was conducted in artificial environment.The results indicate that welding at high temperature and in high humidity ambience results in higher delayed cracking tendency than welding at 0℃.In the highest humidity ambience the delayed crack of Cu-age-hardening steel could be prevented by preheating or keeping the inter-pass temperature higher than 45℃ for gas metal arc welding.