Abstract: Solving the corresponding route stake number of the point outside the route is a common problem ,and is also the basis for the interchange nose point designing program .The quality of the algorithm has immediate impacts on the overall program's efficiency .Based on route stake coordinate calculation and point to the tangent line at any point of the pedal algorithm ,this paper puts forward a new algorithm ,which can be applied to all kinds of complex horizontal a-lignment and neglects the initial stake .The algorithm can one-off search multiple corresponding route stake numbers , which provides an important basis for the interchange program design .