Abstract: In this paper, the dynamic and static strain aging, the tendency of welding hot straining embrittlement of butt joint of double V groove with root face and the influence of strain aging on COD and Charpy impact of transverse and longitudinal weld of 15MnVNq steel butt joint with 56mm thick plates are investigated. Results show 15MnVNq steel butt weld has an obvious tendency towards dynamic strain aging. The sensitive temperature range is about 200~300℃. The most embrittled region of the butt weld is the last bead of the first finished side in welding by both sides. The test results show that it is necessary to use strain aged samples for judging quantitatively the low temperature toughness for welded structure under low temperature working condition.