With the challenges in monitoring marine environmental pollution, developing in situ energy harvesting technologies for self-powered marine sensing nodes has become increasingly urgent for effective environmental protection. As an effective approach for distributed energy harvesting, triboelectric nanogenerators (TENGs) hold significant potential for harvesting high-entropy energy in remote areas. However, the performance of TENGs in practical applications is constrained by the harsh and unpredictable conditions of marine environments. Herein, we propose a flexibility-pneumatic energy storage strategy (F-PESS) for stable output of irregular wave energy. The flexibility allows TENGs to adaptively deform to accommodate variable wave conditions, while the pneumatic energy storage ensures a stable output. Additionally, a four-helix structure is designed for converting disordered wave energy into a high-frequency, bidirectional output. Utilizing this strategy, the TENG device can attain up to 67.7 μA of current output, produce 17.94 mW of power, and deliver a power density of 34.26 W m−3. After employing a power management circuit, the system achieves a pulse current output of 1.28 A. Importantly, a self-powered marine hydrological monitoring system is implemented, illustrating the feasibility of the proposed F-PESS. This work presents a potential solution for progressing irregular wave energy and the implementation of self-powered monitoring sensor networks in marine environments.