AbstractIn this study, using a hydraulic system couples 2 hydrofoils and fulfills the fully flow‐induced oscillating motion. Two hydrofoils have a tandem spatial configuration because in such arrangement allows the turbine to reach a higher efficiency. An iteration scheme is compiled to the solver to solve the coupling equations which are built based on the hydrofoil motions and hydrodynamic. Numerical investigations are carried out to analyze the response of 2 tandem oscillating hydrofoils. The objective of this study is to review the wake interactions between 2 tandem hydrofoils rather than to pursue the maximum power efficiency. It is found that the heaving amplitude and energy extraction performance of the upstream hydrofoil are greater than that of downstream hydrofoil, because the downstream hydrofoil operates in the wake of upstream hydrofoil. For the fully flow‐induced motion model presented in this study, both favorable and unfavorable strong wake vortices interactions are not observed, because the change in system response will weaken the strong wake interaction. Moreover, the difference between 2 hydrofoil responses does not necessarily decline with increasing inter‐hydrofoil spacing.