Abstract: The influence of hot straightening temperature on fatigue properties of S355J2W+N low alloy steel butt joints (without reinforcement)was studied through fatigue test and fractography analysis to specimens which were flame straightened at different temperature.The results show that the hot straightening temperature had a certain effect on the fatigue properties of the joints.The fatigue properties of the joints hot straightened at 800 ℃ was the best and the fatigue properties of the joints hot straightened at 700 ℃ was the worst,which was even worse than those of the joints without hot straightening.So the hot straightening temperature of S355J2W+N low alloy steel butt joints was suggested to be controlled in the range of 800～1 000 ℃.