Abstract: The reheat embrittlement behavior of the coarse grain heat affected zone (CGHAZ) in welded joint of 12Cr1MoVG steel was investigated by means of thermal simulation technique. The results show that the reheat temperature had remarkable effects on the microstructure and properties of CGHAZ. With the increase of reheat temperature, the martensite and bainite in the microstructure decomposed while the ferrite merged, the precipitated carbides increased, gathered and grew up, and the impact energy first decreased and then increased, but the hardness displayed an opposite trend. At the reheat temperature of 630 ℃, the impact energy of CGHAZ had the lowest value but the microhardness hit the largest value, and the reheat embrittlement occured. The reheat embrittlement can be ascribed to the orientational precipitation of intragranular carbides and the occurrence of large granular carbides in the grain boundaries of CGHAZ.