A thermal management system for high-temperature fuel cell mainly comprises a first mixer to introduce external fuel to a reformer, a reformer to adjust the gaseous fuel to a proper composition ratio and output the fuel to the anode input of the fuel cell, a second mixer to introduce external ambient air to the cathode input of the fuel cell, a cathode thermal cycle pipeline to deliver the high-temperature air from the cathode output of the fuel cell to pass through the second mixer and the reformer and also heat the second mixer and the reformer to recover the heat, an anode thermal cycle pipeline to introduce the water steam from the anode output of fuel cell, remaining fuel and thermal energy to the first mixer to mix with incoming fuel, and provide sufficient water-to-carbon ratio and the inlet temperature required for the reformer.