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The mechanical properties of dual-phase steel (DP1000) over the strain rate range of 10-3-103 s-1 were studied using an electronic universal testing machine and a high-speed tensile testing machine. The plastic deformation mechanism was investigated from the perspectives of the strain rate sensitivity index, activation volume and dynamic factors. The results show that the tensile strength and yield strength of DP1000 increase as the strain rate increases. The elongation increases without any change after fracture, and then decreased rapidly when the strain rate reaches 103 s-1. The true strain curves of DP1000 show three stages: the point of instability decreases in the strain range of 10-3-10-1 s-1; the instability point increases between 100-5×102 s-1; above 5×102 s-1, and the instability strain becomes smaller again. The plastic deformation mechanism of the DP was determined by the competitive contributions of work hardening (strain hardening, strain rate hardening) and softening effects due to the adiabatic temperature rise.