Abstract: The welding simulated continuous cooling transformation curve (SHCCT) of S690 QL quenched and tempered steel was plotted by using the welding thermal simulation technology. The effect of heat input and welding pass on the impact toughness of coarse grain heat heat-affected zone (CGHAZ) was investigated. The results show that the S690 QL steel has a high martensite formation capacity, there is still the existence of martensite in CGHAZ when the heat input is 46.5kJ/cm (corresponding to t_8/5=18s). Heat input has little effect on the impact toughness of CGHAZ, the main reason is that the grain size of CGHAZ has little change with the increase of heat input. After multi-pass thermal cycling, the formation of small equiaxed recrystallized grains leads to a significant increase in impact energy of supercritically reheated coarse grain heat heat-affected zone (SCR CGHAZ) compared with that of CGHAZ.