The invention provides a coupled FEM-PE-based sound radiation prediction method of an elastic structure under an ocean channel. Firstly, a multi-physical-field coupling theory model of sound radiationof the structure under an ocean channel environment is established; a finite-element method (FEM) is utilized to acquire a radiation sound field on one-dimensional transversals of a depth direction;and a piecewise cubic Hermite interpolation method is adopted to carry out perfect matching, namely a FEM-PE coupling condition, of FEM sound field information and grid points of a parabolic-equation(PE) method on space, then the radiation sound field information is used as an initial condition of PE finite-difference-method (FDM) calculation, and then quick prediction of the sound field at any field point of the elastic structure under the ocean channel is carried out after setting related parameters of the PE method. According to the method, adaptability on the elastic structure and the ocean channel is high, a calculation result is accurate, efficiency is high, use is simple, and promotion is easy, and many bottleneck problems that large calculation amounts, multiple physical fields, complex channel environments and the like currently encountered when sound radiation prediction of elastic structures under ocean channels are studied are effectively solved.