In this paper, an experimental and numerical study on the flow evolution and energy extraction performance of a flapping-airfoil power generator is conducted, and wide ranges of motion parameters are considered. PIV (Particle image velocimetry) method is used for flow visualization around the flapping airfoil, and numerical simulations predicting the flow field and power generation process are also conducted and compared with the test results. It is found that the computed flow field basically agrees well with the experimental results, and the power generation ability of the power generator is validated. At a fixed plunging amplitude H-0, both the decreasing reduced frequency k at a fixed pitching amplitude theta(0), and the increasing theta(0) at a fixed k lead to larger sizes of flow separation. For the flapping motion studied, both plunging contribution and pitching contribution play important roles in the energy extraction, which is very different from the traditionally imposed flapping profile. Besides, at a fixed k, the increasing H-0 induces a slight increase in pitching contribution, and the increasing theta(0) is beneficial to power generation enhancement. Moreover, the increasing H-0 induces a notable increase in output power at relatively low k, while it has little effect on efficiency enhancement. (C) 2015 Elsevier Ltd. All rights reserved.