Abstract: The dynamic compress properties of air-cooled bainitic 971 steel, which depend on the heat treatment process, length-diameter ratio and test temperature, were investigated with the SHPB dynamic mechanical properties testing system, metallurgical microscope and the S-4800 scanning electronic microscope. The results indicate that the dynamic compression yield strength of 971 steel is increased by 8% with the raised length-diameter ratio when 971 steel went through the tempering at 500 ℃ after normalizing, while increased by 20% through the tempering at 650℃ after normalizing. 971 steel has the low temperature sensitivity, its dynamic compression yield strength at -40 ℃ is lower about 20% than it at room temperature. The inner structure of adiabatic shear band of the hat-shaped sample is denser than outer one with melting appearance and morphology of ridge-like and porous network structure.