<p>With the acceleration of urbanization, the safety of urban underground utility tunnels, as an important component of urban lifeline engineering, has received increasing attention. In this study, commonly used cables (VVR cables) in urban utility tunnels were selected as the research object, and a cone calorimeter and thermogravimetric analyzer were used to detect the combustion characteristics of the cables. The results show that the combustion process can be roughly divided into six different stages, namely ignition, sheath fire, slow spread, rapid spread, full development, and decay. Additionally, an L-shaped utility tunnel numerical model was established using FDS software to study the fire spread law under the coupling effect of different blockage rates and ventilation. The dynamic spread changes of cable fires, heat release rate, temperature distribution, and other internal fire parameter variation laws in the utility tunnel under different blockage and ventilation conditions were analyzed. This study provides valuable insights for understanding the combustion behavior of power cables and effectively offers reliable support for the safe construction of fire prevention and control in urban underground utility tunnels.</p>