Abstract: The large amount of decay heat in a quite long time after reactor shutdown, which is an important characteristic of the nuclear power plants, should be considered seriously during the safety analysis. Therefore, the study on the decay heat and its uncertainty analysis play an important role in the design of decay heat removal system, as well as in the safety verification of the fuel element during the accident. In referenced to the standard of Germany entitled “Decay Heat Power in Nuclear Fuels of High-temperature Reactors with Spherical Fuel Elements” especially for pebble-bed high temperature gas-cooled reactor (HTGR), the calculation method of decay heat and its uncertainty of pebble-bed HTGR were introduced. On the basis of the preliminary physical design of Chinese 200 MWe high temperature gas-cooled reactor pebble-bed module (HTR-PM), the decay heat and its uncertainty after reactor shutdown from long-term operation at rated power were analyzed, so as to provide a basis for further accident analysis.