As a new mode of energy extraction, flapping foils show broad application prospects. How to improve the energy extraction efficiency (eta) of wind or hydro energy with flapping foils has become a focused issue for scientists in this field. This paper numerically investigated the energy extraction of flapping hydrofoil with different NACA 4 and NACA 6 series foil shapes. Firstly, compared with experimental results, the simulation results were validated. Secondly, by adopting different series of foil shapes, simulation was conducted for energy extraction of flapping foils which were moving harmonically in current: (sic) symmetric foils with different maximum thicknesses; (sic) symmetric foils with different maximum thickness positions; (sic) non-symmetric foils with same maximum thickness, maximum thickness position and camber, but different maximum camber positions; (sic) non-symmetric foils with same maximum thickness, maximum thickness position and camber position, but different maximum cambers. It is found that for symmetric foils with different maximum thicknesses, eta basically increases first and then decreases with the increase of maximum thickness; for symmetric foils with different maximum thickness positions, eta first increases and then decreases when maximum thickness position moves from the leading edge to the trailing edge; for non-symmetric foils with same thickness, eta shows lower value with larger camber; compared with maximum camber position, the maximum thickness shows larger influence on eta. (C) 2016 Elsevier Ltd. All rights reserved.