Samples of the Paleogene-Neogene argillaceous rocks in the Dongying and Zhanhua sags of the Jiyang depression have been analyzed on the basis of the X-ray diffraction test of the bulk rock. The studies of organic carbon, porosity and permeability show that detrital minerals are widespread in the, in which the feldspar content is higher. The clay minerals are dominated by detrital clay, and the carbonate content is relatively high in the argillaceous rocks. Flat pores are the main pores formed by micropores and distributed rather evenly in the argillaceous rocks, in which the pore content is higher than that in sandstone. On the whole, the pore structures can be grouped into three basic types, i. e. fine pore throat, thick pore throat and mixed pore throat. The main influencing factors on the pore structures in the argillaceous rocks are considered as follows: (1) the different carbonate contents cause differences in the basic features of the pores; (2) compaction causes the porosity to reduce, and undercompaction protect the pore structure; (3) the abundance and maturity as well as occurrences of the organic matter have close relations with the corrosion pores; and (4) the abundant organic matter is favorable for abnormal pressure to grow, which can protect the pore system.