Abstract: In the practical operation , especially to the carbonate strata , predicting lithological ratio of the object layer between wells or in noOwells regions is realized with seismic velocity information. This article proofreads the systematic errors between the dip and the seismicOacoustic velocity of the velocity spectrum ,and so , the interval velocity information of the original seismic sequence can be dependably gained. On the basis of this , several
models are established : lithological predicting models , interval velocity model of the seismic sequence , compaction model of the high and low velocity layers , geological model , equivalence model , mathematical model. The lithological ratio of the studied layers is quantitatively predicted with these models. On the basis of the studied layer being finally divided into many layers ,and according to the number of different lithological types ,stratigraphical lithology is simplified to binary structure that is
calculated and proofread. Carbonate lithological ratio can be gained in corresponding high velocity layers. The predicting effects are very good to Carboniferous strata in southwest Tarim basin.

Key words: interval velocity, predicting, lithologic ratio, model