Abstract: In addition to reducing the consumption of fossil energy, improving the energy-harvesting efficiency is also one of the key factors to achieve the goal of "carbon peak and carbon neutrality" in China. Flapping wings are simple and environmentally friendly devices that can harvest energy from fluids. To improve the energy-harvesting efficiency of flapping wings, a novel flapping wing with trailing-edge flaps is proposed, whose performance is characterized by investigating the flow fields obtained by numerical simulations. By changing the deflection strategy of trailing-edge flaps, it is found that the continuous deflection in one motion cycle can achieve the most significant improvement in the energy-harvesting performance. Finally, a comparative analysis on the performance of active trailing-edge flaps and passive Gurney flaps is carried out. Results show that, depending on the reduced frequency, both types of flaps can achieve promising performance thus they are potential for future application. The Gurney flaps are applicable when the reduced frequency is in the range (f ^* = 0.08 ~ 0.14), with the maximum efficiency of 41.2% at f ^* = 0.12. By comparison, the trailing-edge flaps perform well in the higher frequency range (f ^* = 0.12 ~ 0.22), with the maximum efficiency of 46.3% at f ^* = 0.18.