<p>With the rapid acceleration of global urbanization, the urban underground comprehensive utility tunnel has emerged as a vital infrastructure component. In the utility tunnel, the prolonged overload or aging of cables increases the risk of electrical fires, which severely threatening the safe operation of these tunnels. In this study, 110&#xa0;kV flame-retardant cables were selected as experimental materials, and full-scale fire experiments were conducted in a real-scale utility tunnel, where the flame spread behavior, smoke temperature, and mass loss of the cables were measured. It was found that the fire spreads horizontally along the outer sheath of the high-voltage cable, while molten droplets fall and burn directly below the cable, forming three-dimensional fire. As the fire source height increased, the total mass loss and burning duration of the cables exhibited the nonlinear change. Moreover, the ceiling temperature prediction model for cable fires in L-shaped tunnels was developed based on the cable fire experimental data. This study enhances our understanding for fire propagation behavior of high-voltage cables in real utility tunnels, providing more accurate data to support safety assessments and fire prevention for the utility tunnel.</p>