Quasistatic and dynamic tensile tests of Q235 steel were performed to study the dynamic tensile behaviors under different strain rates by INSTRON and HTM5020 testing machines. Experimental results show that Q235 steel is very sensitive to strain rates. Both the yield strength and the ultimate tensile strength of Q235 steel increase with the growth of strain rate. The hardening characteristics also vary evidently with the increasing strain rate. The dynamic increasing factors of both engineering yield stress and engineering ultimate stress can be expressed as the function of strain rates by using the CowperSymonds model. Based on the true stressstrain relationship before necking of Q235 steel, the JohnsonCook model is modified to take into account the coupled effect of strain hardening and strain rate.