Abstract: The dynamic characteristics of multi-span non-uniform continuous beams were analyzed by the Bernoulli-Euler beam theory. Based on the basic principle of modal perturbation, the analytical mode functions of uniform continuous beams were used to transfer the differential vibration equation of non-uniform continuous beams to a set of algebraic equations. In the method, the dynamic characteristics of the beams with complicated section types can be solved effectively, whether the section function is continuous or not. The numerical results of two examples show that the method is simple, practicable and has good precision.