Abstract: The translation of microstructure and the toughness of coarse grain heat affect zone (CGHAZ)of 07MnNiCrMoVDR steel were investigated by thermal simulation testing machine which type of Gleeble-3500.The simulation samples were picked up from the perpendicular to the rolling direction of 07MnNiCrMoVDR steel.The experimental results indicate that the bainite and low carbon martensite is the dominate microstructure in the CGHAZ.With the cooling rate decreases, the bainite transformed from upper-bainite to lowbainite.The impact absorbing energy of the CGHAZ is worse through the heat treatment.The brittleness of reheat will probably induce the crack of reheat because of coarse grain boundary carbide precipitation. The greater the cooling rate, the more serious of the reheat embrittlement.