Abstract: To address the challenges of limited mobility and data acquisition in complex maritime environments such as nearshore and island reef areas faced by traditional magnetic survey methods, we developed a hybrid vertical take-off and landing (VTOL) unmanned aerial vehicle (UAV) aeromagnetic survey system suitable for marine applications. The system integrates a high-sensitivity fluxgate magnetometer and a GNSS-RTK/INS integrated navigation module on an electric hybrid VTOL UAV platform. To mitigate magnetic interference generated by the flight platform, compensation processing was conducted based on the T-L magnetic compensation model, and the compensation effectiveness was verified using cross-line data. A data processing workflow from preprocessing, compensation, correction, to leveling was established and validated in flight tests in the experimental area. Results demonstrate that the system's accuracy indicators could meet the technical requirements of aeromagnetic survey and relevant marine investigation standards. This system provides an effective technical support for magnetic surveys in nearshore and island reef regions, showing broad application prospects in marine geophysical survey.