Abstract: An approximate function of the dynamic pressure of liquid in which a beam is vibrating is given by integration of Green's formula, than algebraic equations with symmetric coefficient matrices are obtained from the original problem by variational method. Solving the finite element dynamic equations of the beam coupled with the liquid pressure equations, we can find the solution of the coupled vibration of the immersed baem. Because only the boundary degrees of freedom of the fluid field are left in the liquid dynamic pressure equations, the numeber of algebraic equations is much smaller than that in common finite element method. At the same time, as all coefficient matrices of the equations are symmertrical, the present method is better than the common boundary element method in data storage and computational efficiency.