Keywords: 
• Pre-Caspian basin /
• carbonate rock /
• drowning unconformity /
• high-frequency sequence /
• reservoir facies belts 

Abstract: KT-I is one of the most important oil bearing series in M block of Pre-Caspian basin. The reservoir spreading is not clear understanding with varied types of facies belts, severe  heterogeneity  and limestone interbedded with mudstone. In terms of high-frequency sequence stratigraphy, the feasibility and thought of tract system division in high-frequency sequence and super sequence is put forward. And the drowning unconformity plays an important part as carbonate sequence boundary. On this basis, by the recognition of sequence boundary, such as drowning unconformity and exposed punctuated surface, KT-I member has been for the first time divided into 3 fourth level sequence and 9 fifth level sequence and the system tract of high-frequency sequence has also been done. The system tract model of high-frequency sequence on rapid transgression (equivalent to drowning unconformity) and slow transgression condition has been established. Then, the developing features of strata and the reservoir spreading in study area have been clear. The application of drowning unconformity and the system tracts of high-frequency sequence in carbonate petroleum exploration has been summarized at last.