Abstract: The Mesozoic reservoirs in the Eastern Depression of North Yellow Sea Basin are commonly characterized by very low porosity and permeability. The most important task in the exploration of oil and gas of the basin is to study the secondary pores for finding the high quality reservoirs and favorable hydrocarbon accumulation areas. Combining the drilling, cores and physical property data, using the methods of thin section identification, cathodoluminescence and scanning electron microscope, characteristics of porosity and permeability and pore types are studied in this paper. Secondary pore zones and their influencing factors are discussed. It is found that the development of secondary pores is influenced not only by diagenesis, but also by the material composition, sedimentary facies, stratigraphic unconformity, and structural fractures. The eluviations along the stratigraphic unconformities, weathering surfaces and faults are the most important factors for the formation of secondary pore and improvement of reservoir properties. In sum, the favorable position for the secondary pores is always close to the unconformity surfaces in the middle Eastern Depression of the North Yellow Sea Basin.