Subway is consisted of tunnels, platforms and ventilation shafts. The air flow between these structures forms a ventilation network. There is a need for fire modeling tools capable of both rapid and precise simulation for fire and smoke propagation in such ventilation network. Computational Fluid Dynamics (CFD) is widely used in subway fire performance design. However, the boundary conditions used in models are always assumed to be constant. The interactions between fire and ventilation network cannot be considered. In other word, we only know it is safe under a certain boundary condition but whether the emergency system can run effectively and provide such a boundary condition is unknown. This paper presents a new fire model to solve this problem. TNFIRE3 is a coupling model in which network model is combined with CFD model. Smoke propagation in fire tunnel and air flow in the whole line can be simulated simultaneously. TNFIRE3 capabilities include different kinds of fire sources, radiation, train motion and operations of emergency ventilation system. A demo case of subway tunnel fire has been carried out to illustrate how to design the emergency ventilation modes with TNFIRE3.