Under strong crosswinds, the aerodynamic performance of box car is the worst in the universal vehicles used in the railroad. Using 2D, steady state incompressible Navier-Stokes equation and two equations k-εturbulent model for the box car under strong crosswinds, the optimization of the aerodynamic figure has been carried out by finite volume. Results obtained show that the figure of roof greatly affects the aerodynamic performance of box car. The P₆₅ box car with arch roof has better aerodynamic performance than the P₆₄ box car with slope roof. If the roof arc and the lateral wall could be connected by the round fillet, the aerodynamic performance would be much better. With a consideration of the two factors of aerodynamic performance and the effective volume, it is suggested that the roof arc radius should be 2692mm and the fillet arc radius be 500mm.