The present disclosure relates to the technical field of rail turnouts, and to a method for determining propagation characteristics of guided waves of a variable cross-section rail of a turnout. The method includes the following steps: step 1: establishing dispersion curves: separately calculating dispersion curves of sections of a variable cross-section rail, and fitting dispersion curves of different sections in a similar wave mode according to a longitudinal position to generate a “wavenumber-frequency-position” three-dimensional dispersion surface; step 2: analyzing dispersion characteristics: based on the “wavenumber-frequency-position” three-dimensional dispersion surface, using a semi-analytical finite element method to calculate a wavenumber-frequency dispersion curve and a guided wave structure of the characteristic section; and step 3: performing finite element simulation verification: establishing a switch rail model for simulation, then using two-dimensional fast Fourier transform (2D-FFT) to identify a frequency wavenumber dispersion curve of collected data.