Abstract: The hot gas duct of China 500 MW Pilot High-Temperature Gas-cooled Reactor connects the reactor pressure vessel and the steam generator. The hot gas duct is the main passage of the helium from the reactor core to the steam generator. The hot gas duct is class 3 component in nuclear security standard. According to ASME criterion, it is required that the hot gas duct should keep its integrality during the seism. In order to validate the reliability, the finite element analysis model of the hot gas duct was established and the stress distribution was calculated with the load of the pressure of the insulation fiber, the differential pressure, the gravity and the seism. The calculation shows that the structure strength of the hot gas duct has a large safety margin under the operation load, loss of pressure and seism load.