Abstract: In a 3D isotropic medium,P-wave and S-wave can be separated by divergence and curl operator,but the physical meaning and polarity inversion position will be inconsistent with the original mixed wavefield. The existing method of vector wavefield separation is seeking gradient to the divergence of wavefield and seeking curl to the curl of wavefield once more,which can make sure the position of the polarity is same as before,but the amplitude will be changed. The authors have deduced the formulas of vector wavefield separation in the wavenumber domain,which was based on one-order velocity-stress equation,and gave the concrete solution method combined with finite difference in space domain. The essence of the method was to correct the amplitude of existing vector wavefield separation method by P-wave and S-wave’ s propagation velocity,then regard the correcting result as the second derivatives of P-wave and S-wave respectively. The modeling result of simple model and SEG / EAEG salt model showed that the method could adapt to the vector P-wave and S-wave separation of complex wavefield,and could ensure the waveforms and am- plitude of separated wavefield were same as before.