Abstract: As an important potential structural material for fusion first-wall/blanket application, vanadium alloy (V-Cr-Ti) has been studied a great lot in recent years. In order to study the strain hardening behavior of V-5Cr-5Ti alloy under compressions with different strain rates, especially the twinning effect on the plastic deformation, the strain hardening model of this alloy has been constructed based on the evolutions of dislocation density and twin in this paper. The model considered that the slipping of dislocation in twins could contribute to the plastic strain. The simulation results indicated that strain hardening ratio of dynamic compression, which is smaller than that of quasi-static compression, is caused by dislocation density of the former smaller than that of the latter owing to twinning induced plasticity (TWIP). After the twins formed, the plastic strain rate induced by dislocation slipping increases with strain increasing, and approaches the loading strain rate, while the plastic strain rate induced by twinning decreases with strain increasing.