Abstract: For lock-in condition, the amplitude of vortex-induced vibration on the hydro-mechanical blade/guide vane increases sharply, which can reach 100 times higher than in lock-off condition. Taking symmetric hydrofoils as the research object, numerical simulation of flow-induced vibration under lock-in and lock-off conditions was carried out based on the separated bidirectional fluid-structure interaction and overset grid. The results show that in lock-in condition, the hydrofoil showed a torsional mode shape, and the vortex shedding in the wake area fell off in parallel with the same phase along the direction of the spread; in lock-off condition, the hydrofoil vibrated in the form of beat frequency. The predicted relative difference in the vibration amplitude of the hydrofoil in lock-in and lock-off conditions is basically consistent with the experimental data, which can provide guidance for the evaluation of vibration characteristics under large deformation conditions.