This study successfully fabricated high-performance Poly(vinylidene fluoride) (PVDF) piezoelectric membrane using the Non-solvent Induced Phase Separation (NIPS) method combined with graphene doping technology, specifically focusing on their potential application in ocean wave energy harvesting. The research systematically investigated the synergistic mechanism by which the graphene nanofiller influences the film's rheological properties, microstructure, and the formation of the critical piezoelectric polar phases. Experimental results confirmed that the incorporation of graphene effectively induces the PVDF crystalline transition; however, the resulting piezoelectric output exhibited a non-linear dependence on the doping ratio. Specifically, the optimized doping concentration of 0.75 Gr yielded the highest peak-to-peak voltage of 5.64 V, attributed to the successful maximization of the polar crystalline phase content. This performance optimization strategy was ultimately validated in a simulated ocean wave oscillation tank, demonstrating the film's capability to stably and efficiently convert low-frequency dynamic marine mechanical energy into electrical energy, thereby offering a tangible technical route and potential solution for developing highly efficient and durable green energy harvesters for marine environments.