Abstract: Besides the conventional loads, the accidental loads should be considered on the safety design for the concrete filled steel tube (CFST), and one of accidental events is the lateral impact. According to the stress state of concrete and steel, the constitutive model of RHT is used for the concrete, and that of John-Cook is used for the steel. The damage evolution rules for the inner concrete are studied using the dynamic finite element software of AUTODYN, in the conditions of the impact varied with mass, velocity and the position contacted with CFST, and different restrained types at the ends. The results show the damage begins from the contact position between the impact and the CFST, and develops toward the bottom of an impact position and the restrained end. During the interaction between the impact and the CFST, the strong damage zones are also generated near the restrained end and the zone of maximum deflection. There is a strong damage zone in the upper concrete near the impact position; and the damage characteristics at the end are decided by the restrained type: the strong damage zone lies in the restrained region for the simple support end, and lies outer for the clamped support; the damage distribution in the maximal deflection is controlled by the relative position between the impact and the center of CFST and the restrained type at the end. The inner energy absorbed by concrete increases with velocity, the weight of impact, and the horizon distance between the impact position and the center of CFST. There is a larger plastic strain near the impact position, which may decrease the capacity of resist compression for the impacted CFST. The results are significant to assess the residual capacity of CFST suffered from the lateral impact.