The oscillating hydrofoil of tide energy collection system establishes the movement equation which includes the pitch and the heave. However, the difference of induced drag between the 3D model and 2D model influences the energy conversion efficiency of system directly. Therefore, the paper establishes the 3D trapezoid hydrofoil hydrodynamic model based on the blade element theory. The simulation of the model takes the 3D unstructured gird and dynamic mesh technique, focuses on the effect of trapezoid ratio to the movement and energy conversion efficiency. The results show: Adapting dynamic mesh to simulate the hydrodynamic characteristics of 3D trapezoid oscillating hydrofoil has acquired the same motion as 2D model; The induced drag of oscillating hydrofoil changes the stable oscillating frequency and pitching amplitude and influences the energy conversion efficiency of system; With the decrease of trapezoid ratio, the energy conversion efficiency of oscillating hydrofoil will increase at first and then decline,with the maximum value at point of 0.5. Trapezoid foil design provides a feasible direction for the optimization of oscillating hydrofoil model.