Abstract: The X100 pipeline steel with high deformation resistance was obtained by the critical region accelerated cooling method. The impact energy and microstructures of the heat affected zone (HAZ) specimens prepared by means of welding thermal simulation technology were investigated. The results show that the ultimate strain capability of the X100 pipeline steel with high deformation resistance was strong and the microstructure was composed of bainite and ferrite. The impact energy of the HAZ specimens prepared by weld simulation decreased with the rise of the thermal cycle peak temperature. When the peak temperature was 1 300 ℃, the impact energy reached the lowest value of 247.9 J, which was reduced by 17.3% comparing to that of base material, and then the fracture mode changed from ductile fracture to cleavage fracture. The rise of the thermal cycle peak temperature resulted in the recrystallization and grain coarseness in HAZ microstructure, and then decreased the toughness.