Abstract: Delaminated inversion of a composite beam is investigated by the method of model analysis.The basic equations are built on the basis of elastic theory. The different sizes and positions of delamination are described easily because of the beam being divided into regions. The characteristic equations are established by using the boundary conditions, continuous conditions of the displacements and equilibrium conditions of the shearing force and moment in each region. Considering the first intrinsic frequency and vibrative shape of the system, one parameter is known by resolving the characteristic equations. The theoretical basis is provided for non-damage test in engineering.