As high-voltage cable tunnels are mostly closed underground spaces, a fire in the cable will cause great threat to personnel and equipment. For this reason, this paper constructs a high-voltage cable tunnel model through FDS numerical simulation, and simulates and studies the temperature distribution law when a fire occurs in a high-voltage cable tunnel. The study shows that the temperature in the high-voltage cable tunnel rises slowly before 25 s, rises rapidly after 25 s, and gradually stabilizes after 100 s. The closer the location of the fire source is to the top of the tunnel, the significant increase in the temperature difference in the horizontal direction, at the same time, the fire source power of 6 MW, the temperature of up to 450 ℃, and the larger the power of the fire source, the temperature will also increase. The research results can provide a reference for the safe design and fire protection of high-voltage cable tunnels.