There is a certain functional relation between seismic interval velocity and formation porosity as well as residual porosity.The residual porosity indicates the compaction state of the formations. Hence the sealing capacity of faults can be predicted by seismic interval velocity. The followings are the procedure:(1)to determine relation curves of porosity changing with depth by regressive analysis;(2)to classify the compaction grade according to residual porosity and discriminate fault sealing.This method has been used in Luntai fault in Tarim Basin

and the result is satisfactory.