This paper puts forward an alternative method which deals with the simulation and estimation of urban traffic network. The method is based on Cell Transmission Model (CTM), a macroscopic model for freeway traffic modeling. Some modifications on basic CTM are made to meet the requirement of urban traffic modeling. In order to test the performance of this model, a small virtual traffic network is set up and its simulation results are compared with those of Paramics', a microscopic simulator implemented under similar conditions. Furthermore, a much larger virtual network based on real metropolitan traffic system is constructed and investigated, using which we test the propagation of congestion. We reach the conclusion that our macroscopic model has the potential to depict the general evolution of urban traffic system, and simulate the propagation of congestion within complicated traffic network.