The marine internet of things (MIoT), an increasingly important foundation for ocean development and protection, consists of a variety of marine distributed sensors under water. These sensors of the MIoT have always been highly dependent on batteries. To realize in situ power supply, a flexible seaweed-like triboelectric nanogenerator (S-TENG) capable of harvesting wave energy is proposed in this study. The flexible structure, designed with inspiration from the seaweed structure, processes extensive marine application scenarios. The bending and recovering of the S-TENG structure under wave excitations are converted to electricity. As the output performance increases with the number of parallel connected S-TENG units, an S-TENG system with multiple units could serve for floating buoys, coastal power stations, and even submerged devices. Through the demonstration experiments performed in this study, the flexible, low-cost S-TENG could become an effective approach to achieve a battery independent MIoT.