In remote and harsh sea areas, ocean robots are practical tools to replace humans to execute ocean operations. However, limited power supply constrains the performance of ocean robots, especially in terms of duration time and operation range. Inspired by flying fish, a foldable-wing wave energy converter (FW-WEC) is proposed for ocean robots to extract energy from wave. Equipped with the wave-energy wing, the FW-WEC is capable of switching from the WEC mode that possesses large energy capturing surface to the robot mode with the characteristic of compact structure, which allows for the installation on robots. To satisfy the requirements of the wave-energy wing, several foldable structures are considered and evaluated based on the defined performance index. With the serial four-bar linkage selected and adopted, a prototype of FW-WEC is designed, constructed and tested. The hydrodynamic model is established to analysis the motion response of the prototype under regular wave, of which the accuracy is verified compared with experimental results. According to the wave tank experiment carried out under different wave conditions, the maximum power output of FW-WEC reaches up to 2.6 W and the corresponding capture width ratio is calculated to be 8.0 %. The proposed FW-WEC offers a promising solution for the enhancement of endurance capability of ocean robots.