The exploration of Jiyang Depression has reached in mature or over-mature stage. In view of the increasing of reserve blank area of main oil-bearing beds in mature exploration area，a method，which is suitable for optimizing petroleum exploration target in the main oil-bearing beds of mature exploration area，is established focusing on the Es3 Member in south slope，Bonan Subsag being defined as“seven-step processes”. This method is used to predict the potential of remaining resources in the blank area under the guidance of the“Pareto Geological Probability Model”，and the lithologic structural reservoir is determined as the main exploration target in the south slope according to“Oil and Gas Reservoirs Orderly Distribution”theory. On the basis of fine dissection on“structure，provenance，sedimentation and reservoir”，a fine geological model with multi-source，multi-fan and multi-stage superimposition in blank area is established for the Es3 Member in the south slope，Bonan Subsag. The statistical analysis of reservoir-forming conditions in“9 pictures and 1 table”of mature exploration area is carried out at the same time. The reservoir-forming characteristics of the Es3 Member in the south slope，Bonan Subsag are sorted out，including migration with sand，layer-by-layer distribution，fault sealing，and enrichment with excellent facies. Through comparison of the“positive-negative ratio”between successful and unsuccessful exploration wells，the three major failure reasons for undeterminable reserves are undeveloped reservoir，unsealed fault，and inaccurate oil height. Targeted research is carried out to establish the key technologies in reserve blank area，including the fine reservoir modeling，fault sealing evaluation and prediction of trap oil-bearing height. Through quantitative characterization of reservoir-forming factors，favorable traps are optimized，and exploration deployment is carried out for key targets，and good exploration results are achieved.