This paper presents an augmented network model to represent urban transit system. Through such network model, the urban transit assignment problem can be easily modeled like a generalized traffic network. Simultaneously, the feasible route in such augmented transit network is then defined in accordance with the passengers’ behaviors. The passengers’ travel costs including walking time, waiting time, in-vehicle time and transfer time are formulated while the congestions at stations and the congestions in transit vehicles are all taken into account. On the base of these, an equilibrium model for urban transit assignment problem is presented and an improved shortest path method based algorithm is also proposed to solve it. Finally, a numerical example is provided to illustrate our approach.