Two-dimensional scattering from an arbitrary dielectric target above a rough sea surface is studied by an efficient hybrid method of finite element method combined with boundary integral method (FEM-BIM). The composite model is divided into multiple computational regions depending on energy distribution of an incident wave. With mutual coupling between the target and the dominant region of the sea considered, the finite element method (FEM) and the boundary integral method (BIM) are respectively applied to study the target and the dominant region. Mutual couplings between different subordinate regions are considered approximately by field integral equations based on Kirchhoff approximation (KA). Because FEM and BIM are only performed on the target and the dominant region of the sea, number of unknowns and time required of the new method are reduced dramatically than those of traditional FEM-BIM, making the hybrid method more efficient in the simulation of the composite problem.