The energy harvesting performance of symmetrical flapping hydrofoil varying with thickness, shape and position of pitching axis was numerical investigated via immersed boundary method at a Reynolds number of 1100. The foil performs the given sinusoidal heaving and cosine-curvilinear pitching motions. The center of the hydrofoil is the intersection of the chord line and vertical line at maximum thickness. α is the ratio of the length between the leading edge and the center to the length of chord. β is the ratio of the length between the upper edge and the center to the length of chord. xp is the length between the leading edge and the pitching axis. It is found that enhancing the thickness of the foil can modestly increase the energy harvesting efficiency in the range of 0.03≤β≤0.06, however, it is in contrast in the range of 0.06≤β≤0.105. It is also found that the higher the value of α, the higher the extracting energy when α≤0.4. The optimal foil thickness is β = 0.06. The optimal pitching axis is located at the foil center when α≤0.35, and it is xp=0.35l when 0.35<α≤0.50.The highest energy harvesting efficiency of 41.71% is achieved when α=0.4. •Active flapping foil is simulated using immersed boundary method.•Outline of foil on energy harvesting efficiency were investigated.•The highest energy harvesting efficiency of 41.71% is recorded.