Abstract: In order to solve the conjugate heat transfer problem formed by the guide tube of sodium-cooled fast reactor hydraulic suspended passive shutdown mechanism and the liquid sodium on its inner and outer sides, Trelis, a preprocessing software was used to generate the global high-quality hexahedral mesh, and a solver called chtMultiRegionSimpleFoam of OpenFOAM, which is an open source CFD software, was applied. The temperature distribution results of the numerical analysis of the guide tube were obtained. The results show that the temperature difference in the range of 0.07 m in the circumferential direction of the inner wall of the guide tube is 97 ℃, and the temperature difference in the range of 0.17 m in the axial direction is 80 ℃. In such a narrow range, the temperature difference will generate large thermal stress, and the numerical analysis results of which will provide an important input for the mechanical design of the guide tube.