In the reactor, the axial flow of the coolant into the core causes the rod bundle to vibrate, and the long-term flow-induced vibration will cause fretting wear. In severe cases, the fuel cladding will be destroyed, jeopardizing the efficiency and safety of the reactor. Therefore, the study of the fluid-induced fluid-structure interaction of fuel bundles is beneficial to ensure the safety of the reactor. In this paper, based on computational fluid dynamics and computational structural dynamics, using Euler-Bernoulli beam theory (Euler-Bernoulli), the numerical calculation of fluid-structure interaction is realized by Fluent. And compared with the 5 × 5 fuel bundle without grid.The influences of the rod bundles with or without grids on the fluid pressure, fluid displacement and vibration under different cross-sections are mainly analyzed, as well as the principle of flow-induced vibration in axial flow. The results show that the influence of the vibration of the rod bundle on the flow field is very weak and can be ignored; The pressure difference between the two radial ends of the fuel rod bundle is one of the factors that cause the flow-induced vibration; The existence of the spacer grid aggravates the disturbance of the flow field, so that a larger pressure difference between the two rod bundles causes a larger vibration, and also affects the position where the larger vibration displacement occurs.

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