Abstract: Thermal simulation tests were conducted on 09MnNiDR steel to prepare welding coarse-grained heat affected zone (CGHAZ)samples at different heat inputs by using a Gleeble-3800 thermal simulator.The effect of the heat input on microstructures, hardnesses and impact toughness of the samples was studied.The resutls show that with increasing heat input, the microstructure of the CGHAZ sample changed from lath bainite+granular bainite to granular bainite+massive ferrite, and the hardness decreased.The maximum impact absorbed energy at -70 ℃ of CGHAZ samples at different heat inputs was only 31 J, which did not meet the requirements; the granular bainite structure was the main reason for the deterioration of toughness.With increasing heat input, the grain size of prior austenite in CGHAZ samples decreased and then increased.Therefore, the impact absorbed energy at -70 ℃ of the samples increased and then decreased.