Finite element models of a bus and a barrier were established. By means of mathematical operation, one special type of traffic accident, a bus rolling over and colliding with barrier, was simulated successfully. In both national standard GB/T 17578-1998 and EU’s ECE R66, strength of the top of bus was stipulated. However, simulation made in this paper indicated that the severity of this kind of accident is far more beyond the experiment. To reduce the loss of accident, new material and increased thickness were used for side post of this vehicle, and a following simulation proved its effectiveness, although only to some extent. The results of this paper could be referred by automotive vehicle designers.