In view of the plane heterogeneity of reservoirs and the superimposition of sand body in Weizhou-A Oilfield, Beibuwan Basin, the well data analysis shows that the simple impedance inversion can' t identify sand-mudstone and superimposed sandbody effectively. The lithology impedance was presented in this study by using mathematical transformation method of the P-wave impedance and S-wave impedance. It is proved that the results of lithology impedance are in high coincidence with drilling. The sandstone and mudstone are identified effectively, and the superimposed relationship of sandbody was predicted successfully by using lithology impedance.