By using potential function,the paper introduced an improved analytical method to derive the dispersion equation for Rayleigh wave in layered soils;in accordance with calculation characteristics of the dispersion equation ,it applied a Bisection technique in Frequency-Wavenumber domain to find quickly and accurately the eigenvalues of the dispersion equation; through the study on multimodes dispersion curves of different kinds of layered soils,it modified the statement about that the improved-analytical-method is not an effective solution for middle-soft and middle-hard layered soils; finally, the paper compared the dispersion curve with other curves. The results show that the improved-analytical-method can reasonably analyze the dispersion characters of rayleigh wave in layered soils.