Abstract: The welding process of Q1100 high-strength steel was simulated with Gleeble-3500 thermal simulator, and then SHCCT(simulated HAZ continuous cooling transformation) diagram of the steel was obtained by using thermal expansion measurement combined with microstructure analysis and hardness testing. The microstructure transformation characteristics and hardness change rule of coarse-grained heat-affected zone (CGHAZ) were studied at different cooling rates. The results show that, the austenitizing temperature of the steel in simulated welding condition was significantly higher than that in the equilibrium state. The CGHAZ was full bainite when the cooling rate was under 2℃·s^-1, a mixed microstructure of bainite and martensite was obtained when the cooling rate was 2-12℃·s^-1, and the CGHAZ was full martensite when the cooling rate was over 12℃·s^-1. The hardness of CGHAZ increased gradually with the increase of cooling rate.