The radiation of fire source and hot flue gas plays a very important role in the process of smoke movement. The radiation effect, which was little included in the earlier studies, was included in the present work. So the thermal radiation characteristics caused by two fires will be studied in a tunnel combined with multi-layer zone (MLZ) model, small-scale experiments and numerical simulations. Based on the data obtained by the aforementioned methods, research on the thermal radiation model is carried and a piecewise fire source model is proposed. Subsequently, the longitudinal thermal radiation model caused by two fires in a tunnel is investigated and then modified and verified. The results showed that the thermal radiation model caused by two fires for MLZ model in a tunnel is reliable, which can make a general and reliable judgment on the immediate fire disaster situation, and can also provide reference for the follow-up work.