Abstract: Considering the competition among different transportation modes, a transit assignment method with capacity constrains was proposed. Then, a nonlinear model was established to optimize the running speeds of intercity railway trains. The objective of the model was to minimize the total passenger and operational cost. A genetic algorithm was used to solve the model. Numerical results show that the proposed model can work well on speed optimization problem of intercity railway trains with speed-limit constraints. With the decrease of running speeds in speed-limit sections, the optimal speeds of intercity railway trains rise in sections without speed-limit. For short-distance corridors, a higher running speed can attract more passengers; while for middle-distance corridors, a lower running speed can reduce energy consumption.