Based on the discussion about the effects of free-surface on the incident shear wave,this paper first puts forward a method used to treat the S-wave splitting data outside the critical window.After correcting the amplitude and phase of vertical and radial components,authors analysed the data by using the greatest characteristic values and waveform discrimination operator method,and also analysed explosion data in Tianshui area of Gansu.It may be seen the data show the seismic phase of S wave and S wave fission.