Abstract：Compressional wave can be separated from shear wave in the following steps:Use the zero-stress boundary condition on the free surface to deduce the relation between horizontal or vertical-component displacement and the displacement of compressional or shear wave arriving at the ground surface;Convert the two-component seismic data into those in slowness-frequency domain，then obtain compressional and shear wave fields on the ground surface by using velocity in surface layer;Reconvert them into time-space domain to achieve the separation.Theoretical computation brings excellent separation，and hopeful result can be seen in real data processing.
