Abstract: Classification station plays an important role in railway transportation. It faced various possible schemes when marshaling station would be extended. Decision makers were concern to how to choose feasible extension scheme so as to minimize the total investment. Based on the actual development, optimization model of extension of classification station is built. The objective function is to minimize the total investment, subject to three groups: First is the sorting capacity is to meet the demand, second is the utilization of sorting capacity is not too low, the last is the capacity of feasible scheme should e is larger than former. In order to reduce the difficulty of solving model directly, this model is transformed into shortest path model. The specific solution is expounded through an example application. The use area of the model is described in the end. The model can be used in the macro-control by high-level leader. The specific micro-operation can be done in this decision.