Abstract:In order to derive S-wave velocity from seismic data,we take the presumption of one-dimension layered medium,and use known P-wave velocity and medium density,which were got by using the methods in reference [2],(the density can also be obtained from empirical formula of the given area). The seismic data which underwent plane wave decomposition (τ-p transfrom) are taken as input data,from which the S-wave velocity can be derived with the aid of the simulated annealing method. Theoretical and borehole data trials show that we obtain very accurate S-wave velocity when no error exists in P-wave velocity and density,and that we estimate rather accurate S-wave velocity when P-wave velocity has slight error.