Abstract：Time-distance curve of P-S converted wave is non-hyperbolic,and this characteristic is very obvious when the offset is much bigger than the depth. If the P-wave NMO-correction formula is applied to the NMO correction of P-5 converted wave in the velocity analysis,the shallow seismic data of big-offset traces can not be nicely corrected to result in unfavourable influence on velocity analysis and following stack image. The past measure is only to mute the poorly corrected data of big-offset traces. In the paper,three-parameter velocity analysis formula for P-S converted wave is derived from Castle's three-parameter velocity analysis formula of P-wave. This P-5 wave velocity formula offers accurate velocity,which can be used to achieve good NMO correction of the seismic data of big-offset traces.
