<p>This study utilizes numerical simulations to investigate the maximum ceiling temperature in inclined tunnel fires under natural ventilation, focusing on the impacts of the slope and the cross-sectional geometry of the tunnel. The findings demonstrate that the chimney effect induces longitudinal airflow along the tunnel slope, facilitating smoke exhaust through the upper tunnel opening and causing upward flame tilting. As the tunnel slope increases or the cross-sectional area decreases, the intensified chimney effect results in a substantial decline in maximum ceiling temperature. Furthermore, the Coanda effect, whose strength varies with the aspect ratio of the tunnel, modulates flame behavior and smoke flow. In narrow tunnels with an aspect ratio of 1 or less, the enhanced Coanda effect encourages longitudinal flow and strengthens the chimney effect. In contrast, in wide tunnels where the aspect ratio exceeds 1, lateral smoke diffusion diminishes this effect. Piecewise empirical models are proposed to predict the induced airflow velocity and maximum ceiling temperature under the condition of bidirectional smoke overflow. These research outcomes offer essential guidance for optimizing fire safety designs, refining smoke control strategies, and improving emergency response protocols in tunnel engineers.</p>