Abstract: A large quantity of Ordovician krast caves in Lunguxi (LGX) region of Tarim Basin act as krast vugs to hold oil and gas, exerting a great influence on the productivity in this region. The drilling results showed that oil and gas in this region were distributed mainly less than 50 meters below the top surface of buried hill. However, krast caves are seriously packed in this area. On the conventional seismic profile, the caves both packed and unpacked show ^“beaded^” reflective characteristics. It is difficult to identify the effective reservoir by means of a single geophysical method. Based on observation of cores from a number of wells in the operational zone and combined with the geophysical response characteristics and forward model, the packed krast caves under different cap-rock conditions were distinguished. The reflective characteristics of effective reservoir can be identified with the help of frequency spectrum analysis technology. This method has achieved good results in actual application.