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The subject of the interest is applied of non - destructive vibration method to identification of beam’s damage. A beam described according to the Bernoulli - Euler theory with variable cross sectional area has been analysed. These type of beams are often used in the design of aircraft, robot arms and tall buildings. Identifying structure damage at an early stage has influence on the cost of repair and has impact on safety. In the paper symmetric cracks have been localized at points of the beam’s length. Proposed method is based on the knowledge of the same number of vibration frequencies of undamaged element and the knowledge of the same number of vibration frequencies of an element with defect. The number of known frequencies depends on the number of searched parameters of one or more cracks. To determine of the values of free vibration frequencies the analytical solution, with the help of the Green’s function method, has been used. The results obtained from the theoretical model have been compared with the results from the commercial program using the finite element method. The presented method can be successfully used for the identification of damage of real objects.