Abstract: Seismic inversion is one of themost important core techniques in quantitative prediction of thin interbed reservoir. The information of both acoustic log and other log, which is sensitive to lithology, is used to construct quasi-acoustic logs. The quasi-acoustic logs can not only reflect the variation of interval velocity and impedance, but can resolve some problems like identifying lithologic character, differentiating thin layers, etc. The difference between sandstone velocity andmudstone velocity is in Qikou sag is too weak to be used to predict reservoir, therefore, the quasi-acoustic log of SP log, which is in accordance with lithology, are used in inversion, i-deal effects have been obtained in identifying the distribution and the thickness of reservoir.