This study analyses the dispersion characteristics of guided waves in rails. The semi-analytical spectral element method is proposed, and the finite element model of guided wave propagation in rails is established. Firstly, the spectral element method was used to improve the traditional semi-analytical finite element method, and the characteristic equation of waveguide structure was obtained. Secondly, based on the characteristic equation, the dispersion curves of an aluminum plate were calculated, and the dispersion characteristics of guided waves were analyzed. By comparing with the analytical solution of the aluminum plate, the accuracy of semi-analytical spectral element method was verified. Subsequently, the guided wave simulation model of the rail was established, and the dispersion characteristics of the guided wave in the rail were investigated. Finally, guided wave experiment for the CHN60 rail was carried out by RITEC RAM-5000 SNAP nonlinear high-energy ultra-sonic wave experiment system. The experimental results show that the group velocity obtained by the proposed method is highly consistent with the group velocity measured by experiment, and the relative error is only 0.99%. Hence, the semi-analytical spectral element method has high accuracy and feasibility in the analysis of guided wave dispersion characteristics of the rails, which provides a theoretical basis for guided wave damage detection in rails.