Abstract: J Oilfield, a typical complex fault block oilfield with medium-deep burial depth in Bohai Bay Basin, is characterized by low degree of overall proved reserves, scattered distribution of potential reserves and increasing difficulty in the evaluation. Based on the comprehensive analysis of relevant drilling, core, logging, pressure and seismic data, the authors carry out the comprehensive study of reservoir, explicit the source direction of Shahejie Formation, controlling factors in sedimentation and the distribution rule of reservoir. Combined with the analysis of regional accumulation conditions, oil and gas distribution in J oil field, 4 kinds of potential areas accumulation models i.e. oil-gas reservoir in the adjacent fault block, in the interlayer, in the edge and recovered from water layer are summarized in J Oilfield. In view of the reservoir and the potential distribution in J Oilfield, 6 kinds of potential and evaluation model are established and successively applied in the evaluation of 13 potential oil-saturated layers and 3 fault blocks with exploration potential. As a result, 6.5 million tons of proven oil geological reserves has been increased, 15 adjustment wells after optimizing and adjusting are deployed, and one million tons of recoverable reserves to be increased can be expected. Meanwhile, good economic benefits are also achieved.