For the hypersonic vehicle whose inlet and combustion chamber are not on the same axis, the S-duct is an important component, and its main function is to turn the air flow. However, the existing researches mainly focus on the flow field of S-duct, and few study the creep under the multi-field coupling effect of S-duct. In order to study the influence of multi-field coupling effect of creep material on the S-duct of hypersonic inlet, the numerical simulation of the S-duct of hypersonic inlet for long endurance was carried out by using the independently developed fluid-solid-thermal bidirectional coupling calculation and analysis platform. Firstly, the accuracy of the coupling platform is verified by the creep stretching calculation example and the heating experiment of the stainless steel round tube. Secondly, the stress relaxation caused by creep is analyzed. Finally, the influence of multi-field coupling calculation considering creep on flow field is studied. The results show that the location of the maximum creep strain in S-duct is changing, and the creep effect will lead to the relaxation of S-duct stress and affect the stress distribution and magnitude of the structure. The creep effect changes the solid structure of S-duct, and influences the wave structure, pressure and temperature of flow field under the multi-field coupling effect. Therefore, it is necessary to consider the creep effect of materials in the multi-field coupling calculation of S-bend of hypersonic inlet for long endurance.