Abstract: The discovery of high porosity and high permeability reservoirs has changed the traditional understanding about reservoir quality in E₃s² in A structural area, Bohai Sea. On the basis of the drilling core and the laboratory analyzing results, study has been conducted on the lithologic characteristics, sedimentary genesis, reservoir characteristics and influence factors on this type of reservoir. The study results indicate that this type of reservoir was mixed deposits, affected by intermittent local terrigenous supply, and the sedimentary facies is the main factor influencing the reservoir quality. In addition, the later mixed dolomitization has some positive influence on reservoir quality protection and improvement.