In the optimization of train diagrams,selecting the arrival and departure paths of the through trains has a great impact on the dwell time at district stations. In this paper,on the basis of train paths and the through train connection time standard at district stations,we built a mathematical model aiming at minimizing dwell time of through trains at two adjacent district stations,and then converted this into a network flow model to which is added a source and a sink node. Then,we propose a new algorithm for solving the network flow model based on the minimum-cost flow algorithm. A case study for through trains from the Guiyang South Railway Station to the Chongqing West Railway Station shows that the algorithm is reliable and efficient for solving the problem of through train connections,and there is a reduction in the total dwell time that the through trains spend at two adjacent district stations. In the optimization of train diagrams, selecting the arrival and departure paths of the through trains has a great impact on the dwell time at district stations. In this paper, on the basis of train paths and the through train connection time standard at district stations, we built a mathematical model aiming at minimizing dwell time of through trains at two adjacent district stations, and then converted this into a network flow model to which is added a source and a sink node. Then, we propose a new algorithm for solving the network flow model based on the minimum-cost flow algorithm. A case study for through trains from the Guiyang South Railway Station to the Chongqing West Railway Station shows that the algorithm is reliable and efficient for solving the problem of through train connections, and there is a reduction in the total dwell time that the through trains spend at two adjacent district stations.