Abstract: By using the calculus thought, based on the traditional graphic method and the law of conservation of energy, this article started from a new point of view to establish the calculation model, taken the instant speed and time that the vehicle humped to an arbitrary point of the railroad as a direct inspection target, calculated the interval of key points indirectly. The results could be compared with the original design. The computer program was based on ObjectARX to the secondary development of AutoCAD. After testing, the results obtained by this method could be proved by the results of the original design.