Abstract: Round-ended concrete-filled steel tubular (RE-CFST) members have been employed in bridge structures owing to their advantages of low fluid resistance coefficient, high load-bearing capacity, and excellent ductility. To investigate their impact resistance subjected to vehicle collisions, six RE-CFST columns were first tested to assess the deformation modes, impact forces and mid-span deflection histories under different impact velocities and axial-load ratios. Subsequently, the FE results were calibrated based on the LS-DYNA software. A total of 36 finite element (FE) models of RE-CFST bridges subjected to vehicle collisions were established, and mechanism analysis and parameter study were conducted, with a primary focus on the effects of sectional aspect ratio, steel ratio, as well as vehicle mass and speed. Finally, according to the residual deflection at the mid-height of piers, a calculation formula of performance index was proposed for designing vehicle-collision resistance for RE-CFST piers. The results indicated that RE-CFST columns primarily exhibit global flexural deformation under drop-hammer impact, and the steel tube and core concrete work together well. The impact resistance of RE-CFST columns decreases when the value of axial-load ratio is larger than 0.2. According to the development of the impact force, the process of vehicle impact on RE-CFST piers can be divided into four phases: head affecting phase, engine affecting phase, cab crushing phase, and trailer affecting phase. The engine impact and cargo impact have significant effects on the dynamic response of piers. When subjected to the vehicle collisions, the internal force distribution within RE-CFST piers corresponding to different impact phases varies significantly. The maximum positive bending moment and maximum negative shear force occur at the impact position and the bottom of the piers, respectively. Moreover, bending moment and shear force also exist at the top of the piers. The performance index of Δ_r,mid/H can be used to assess the damage level of RE-CFST bridge piers subjected to vehicle collisions. In addition, the proposed calculation formula could accurately predict the performance level of RE-CFST piers under vehicle collisions.