Abstract: The conjugate heat transfer was conducted using the fluid dynamics software Fluent to simulate thermal-hydraulic characteristics of the argon space and related structural components of the China Demonstration Fast Reactor (CFR600), and the thermal design of the pump support structure in the argon space was verified. Calculation results show that the prototype design of the pump support structure in the argon space has a large temperature gradient in the circumferential temperature distribution. The temperature of the pump support structure near the support diameter side of the main vessel is significantly higher than the side away from the support diameter. It is shown that the circumferential temperature gradient of the pump support structure is reduced by the improved structural design, which will provide technical support for optimizing the design of the pump support structure.