The mode shape functions of the elastic beams with concentrated mass and stiffness and their frequency equations under typical boundary conditions are derived with Laplace transform. Using these equations, the inherent characteristics of a cantilever beam with a spring and lumped mass are obtained. Then, its modal parameters are recognized using the NExT-ERA(eigen system realization algorithm based on the natural excitation technique) method. The analytic and experimental results show that modal parameters change with the stiffness and location of the mass and spring.