To determine the temperature distribution pattern of the U-shaped tunnel ceiling and the downstream smoke spread behavior under different fire source positions, a full scale U-shaped roadway model composed of a main transport tunnel and connecting tunnels was established using the fire dynamics simulation software(FDS). A full-scale model of the U-shaped tunnel was established using FDS. The tunnel was divided into three sections: A, B, and C, and the fire source position was set at the midpoint of the longitudinal centerline of the different sections of the tunnel. The results show that under a certain heat release rate, the minimum critical ventilation velocity is required when the fire source is located closest to the exit of the tunnel, and the maximum critical ventilation velocity is required when the fire source is located at the longitudinal center of the tunnel. Theoretical analysis of ventilation resistance at different fire source locations was conducted, and specific values of ventilation resistance were calculated for further research. At the same position, the temperature of the ceiling in front of the U-shaped roadway corner is higher than that of a single straight roadway, while the temperature of the roof behind the roadway corner is lower than that of a single straight roadway. Moreover, the temperature of the ceiling decays very slowly near the first roadway corner from the fire source, revealing the distribution law of the temperature of the U-shaped tunnel ceiling.