Abstract: The decay tank is the main component of the pool type low temperature heating reactor. It is used to ensure that the residence time of the radioactive cooling water from the core outlet is more than 100 seconds in the decay tank, so that the short period radionuclide is greatly decayed in the pool. Thus, the level of radioactivity in the primary circuit is significantly reduced. According to the overall layout requirements, the structure of the tank cylinder is an irregular fan-shaped structure, and a splitter plate and an orifice plate are disposed inside. The design work mainly includes the structural design, cooling water decay time calculation and strength analysis calculation of structural parts, and the design is optimized through relevant calculation results. The final design results show that the structural design of the decay tank meets the functional requirements, the decay time of the cooling water in the decay tank is more than 100 seconds, and the strength analysis calculation meets the design requirements.