Abstract: In this paper, inverse analysis of multiple parametric vibration of composite beam with across-the-width delamination is investigated. The basic equations, including the transverse shear, are built on the basis of elastic theory. The different sizes and position of delamination are described easily because of the beam being divided into regions. The characteristic equations in inversion are established by using the boundary conditions, continuous conditions of the displacements and equilibrium conditions of the shearing force and moment in the each region. The initial value of the main parameter is inversed by the characteristic equations and the other parameters are given by searching step by step and making the minimum of the square root of the square difference of the vibrative amplitude. The theory and method is the basis of non-destructive test in engineering.