Based on Euler-Bernoulli beam theory, segmented beam model, and separation variable method, a new method for analyzing the natural frequencies and vibration modes of any multi span and unequal span continuous beam is proposed on the basis of considering the boundary and displacement continuity conditions of the continuous beam, which can be used to efficiently obtain the natural frequencies and vibration modes of arbitrary unequal span continuous beams. This method will provide new ideas and convenience for the study of forced vibration response such as multi-span continuous beam vehicle-bridge coupling.