Abstract：The difficulty of velocity analysis in prestackmigration lain on iterative update of velocity model. Based on two different velocity evaluation methods一depth focus analysis and dual-parameter to-mographie image and through time shift,the paper uses Kirehhoff depth migration to yield depth focus analysis panel and uses tomographic imaging method on common-reflection-point (CRP) gathers to modify the velocity and depth models，that not only overcame the limits of the basic hypotheses (reflection in small angle，short offset and simple overburden)used by model-modified formula in common depth focus analysis，but also deduced a new method for seismic velocity evaluation and modification. The method gained residual moveout by focus depth analysis and CRP ray-tracing,which avoided tedious pick-up of travel-time in prestack reflection tomography. The computation results of numeric models showed that the method presented by the paper has good adaptability and processing effects in the areas having laterally rapid variation of velocity and complex overburden that common velocity analysis methods are difficult to handle.
