Abstract: Thermal physical simulation test was carried out to simulate heat-affected zone of BWELDY960Q steel. Under different peak temperature, the change of microstructure and properties were studied. The results show that each microzone in heat-affected zone has different structure form. It exhibits lath martensite in coarse grained region, and fine lathe martensite in fine grained region, martensite and sorbite in incomplete annealed zone, tempered sorbite in tempered zone, respectively. Original austenite grain begins coarsening when peak temperature reaches 1 200 °C, coarsening phenomenon becomes more significant, while the zone is close to fusion line. Impact toughness of coarse grained zone is decreased by 82.17% of the base metal, it is also found that the toughness loss of intercritical heat affect zone is 46.53%. Compared with the practical welding, heat affected zone obtains more coarse microstructure after welding thermal simulation test.