The invention discloses a composite wave-absorbing material suitable for marine environment and a preparation method thereof as well as application. The material comprises 85%-95% of iron-based amorphous materials and 5%-15% of hexagonal BCN ceramic, wherein the iron-based amorphous materials comprise the following components of, in percentage by weight, 27% of Cr, 4% of B, 4% of Si, 5% of Cu, 7%of Ni, 8% of Mo, and the balance Fe; the hexagonal BCN is prepared by a pyrolysis method to form a single-layer or few-layer structure hexagonal BCN, the preparation method comprises the following steps that firstly, raw materials for preparing the iron-based amorphous materials are added into a vacuum air atomization furnace for smelting, atomizing and powder screening is conducted, then the iron-based amorphous powder is fully mixed with the hexagonal BCN to obtain the powdery composite wave-absorbing material; and the composite wave-absorbing material is prepared by adopting a supersonic flame spraying technology to obtain the wave-absorbing coating suitable for the marine environment. According to the composite wave-absorbing material, a wave-absorbing coating can obtain good wave-absorbing performance, be good in bonding strength with a matrix and excellent in corrosion resistance, and the composite wave-absorbing material is suitable for severe marine environments.