The thermal radiation is the main factor affecting internal thermal flow field in a tunnel. This paper studies on two open ends of a channel inclined with angles of 10°, 20° and 30° by experiments and numerical simulations. The experimental data agree well with the predicted results by using Large Eddy Simulation (LES) to solve N-S equations driven by the buoyancy flow. And the influence of thermal radiation on thermal flow field of tunnel with inclination angles from 10° to 30° at same heat source is obtained by comparing the experiment results and numerical resolutions of coupled with radiation model and without radiation model. Thermal radiation makes temperature near the upper wall of tunnel drop, and the influence of thermal radiation on bottom end of tunnel declines with the inclination angle increasing. However, the inclination angle has a little effect on temperature near the ceiling of the top end of tunnel. Simultaneously, the higher temperature zone leaning to the top end due to the thermal radiation is obtained, and the temperature at the bottom of the upper part of the tunnel increases. The findings of the study are important references for theory research of thermal flow field in inclined tunnels.