Abstract: The room temperature tension tests at strain rates of 0.003 s^-1 (quasi-static) and 20-700 s^-1 (dynamic) were conducted on DP590 steel sheet and CR340LA steel sheet, and then the dynamic tensile deformation behaviour, strain rate sensitivity and dynamic fracture behaviour of tested steel sheets were studied. The results show that no yield platforms were observed on the dynamic true stress-true strain curves of the two tested steel sheets. After yield, the true stress increased rapidly and then slowly with increasing true strain. The effect of strain rate on yield strength was bigger than that on tensile strength, and the strain rate sensitivity and hardening coefficient of DP590 steel sheet were higher than those of CR340LA steel sheet. The uniform elongation of the two tested steel sheets decreased with strain rate increasing. With increasing strain rate, the dislocation density in DP590 steel sheet increased, and dislocation cells formed at strain rate no less than 200 s^-1. Obvious necking occurred during quasi-static stretching of DP590 steel sheet, while no necking occurred during dynamic stretching. With increasing strain rate, the amount of C-shaped dimples on the tensile fracture of DP590 steel sheet decreased, and the amount of equiaxed dimples increased.