For relieving the peak hour congestion in metro network and inducing part of passengers to take a less crowded route effectively to optimize the distribution of network passenger flow, capacitated sections in the network were identified firstly by calculating their load factor. Then an estimation model was constructed considering constraints of time and route and an iterative algorithm was designed to calculate the passenger flow composition of capacitated section in the metro network. The passenger flow composition was classified according to the characters of orgin and destination(OD). Capacitated section Caoyang Rd.Longde Rd. in Shanghai metro system was selected as a research object. The passenger flow composition resulted in the congestion of Caoyang Rd.-Longde Rd. during the morning peak period 8:30~9:00 is obtained. The results have verified the feasibility of the model and algorithm proposed in this paper.