Abstract: In this paper,the effects of stress relief tempering on the HAZ toughness in HSLA steels are investigated.The results show that the secondary hardening decreases the HAZ impact toughness of 15MnMoVNRe steel after tempering.Moreover,the temper brittleness at high temperature is another more important cause to decrease the HAZ toughness fcr HQ80 steel.The smaller heat input,the more their relative loses of toughness are.As for STE609 steel,in spite of slight secondary hardening,the HAZ toughness is improved due to the dissolving of the structures transformed at low temperature and the decrease of distortion in the crystal lattice after tempering at 600℃.The large healt input,the mere obviously the toughness is improved.