Abstract: The heat affected zone (HAZ) simulation test was done on two sorts of 12Cr1MoVG specimen. One of which was ferrite and pearlite for base metal and bainite for the other, by using Gleeble Thermal-force simulation machine. Then, for studying the reheat cracking susceptibility in the two different weld structures, the tensile test was done on the two different HAZ structures at different high temperatures slowly. The result showed that when HAZ structure is ferrite and bainite,its reheat cracking sensitive temperature range is 640-760 ℃ and the most sensitive point is 690 ℃ in our study. When HAZ structure is bainite,reheat cracking tendency is obvious after 650 ℃, especially at 690 ℃.Analysis result showed that when bainite exists in HAZ,its reheat cracking susceptibility is high. However, 5% to 8% ferrite exists in HAZ can reduce the reheat cracking sensitivity.