Abstract:In the case of slant subsurface interfaces,dynamic correction velocity for CMP trace gathers of 3D seismic data depends on to,position and observation direction (sourec-receiving line direction). In order to achieve good dynamic correction,we must do three-parameter velocity analysis, namely determination of three-parameter velocity informations of subsurface reflector:dip direction,dip angle and mean square-root velocity.The iteration algorithm for three-parameter velocity analysis fully uses 3D seismic data to derive the dip direction and dip angle form stacked trace gathers and to determine the mean square-root velocity by scanning CMP gathers,thus reducing the uncertainty of solution and minimizing interpretation. This method needs directional velocity computation,followed by spatial interpolation,azimuth and dip interpotations being convenient.It has been practically shown that this method improves 3D seismic data processing.