Since solving the dispersion characteristics of complex waveguide structure it’s difficult, such as rail, this paper takes the method of vibration modal analysis to extract the propagation characteristics of ultrasonic guided wave. Base on the principle that vibration characteristic frequency and wave solutions could transform into each other, the solutions of frequency characteristics obtained from vibration modal analysis convert into wave solutions, and then extract the dispersion characteristics of the rail. Deformation information from vibration analysis of structure, and wave structure of ultrasonic guided could be calculated. Analysis disperse information and wave structure information of low-level model ultrasonic guided wave, select the type of ultrasonic guided model and frequency range, all these will be used as a follow-up study of theoretical support of designing of special ultrasonic guided wave sensor and testing of experimental.