Abstract: The harden quenching tendency and cold cracking susceptibility of Q890 steel was investigated by welding thermal simulation,maximum hardness test and calculation with empirical formula. The results show that the empirical formula established by Michio Inagaki was more suitable to calculate the cooling time t_8/5 during thick plate welding than D·Vwer's theoretical empirical formula. The coarse grain zone in the heat-affected zone (HAZ) of Q890 steel joint had strong harden quenching tendency,controlling the preheating temperature and welding heat input had little effect on improving the harden quenching tendency. However,preheating could significantly increase the welding cooling time t100 and reduce the cold cracking tendency of the steel. Through data fitting,the relationship between the cooling time t_8/5 and the hardness of coarse grain zone in HAZ was established and had been verified to predict the maximum hardness of Q890 steel.