Smoke control is a key issue in tunnel fire accidents. While jet fans have been widely used in road tunnels, mobile fans provide a good complement, due to its flexibility to operate, especially if there are no fixed jet fans present. To confirm the feasibility of a mobile fan system, full scale fire tests were conducted in Kalldal tunnel in Sweden, with fire size in the range of 1–2.6 MW and a mobile fan placed at the tunnel portal. In the tests, it takes about 4–5 min to establish full flow in the opposite direction and the final flow velocity can reach 1.5–1.9 m/s. To describe the transient behavior of flow development inside tunnel, a one-dimensional lumped theoretical model has been developed. The model takes into account the pressure losses of external wind, the stack effect of fire and friction losses over tunnel walls and two portals. The model is validated using the data from Kalldal tunnel fire tests. Results show that the model can well predict the initial and final steady state velocity, but underestimates the flow development. The model gives prediction on the safe side.