The microscopic pore structure characteristic and its genetic mechanism of Chang 8 oil layer in the Jiyuan region are analyzed by making full use of normal thin section, casting thin section, physical property analysis and mercury injection data. The results show that sediments experienced compaction, cementation, dissolution and fracturing diagenesis during the geological history, which had significant effect on pore structure characteristics. The heterogeneity of diagenesis led to difference between macroscopic physical property and microscopic pore structure. The effects of compaction, cementation and dissolution on quantitative control of pore structure parameters such as displacement pressure and sorting coefficient can be illustrated, through calculation of apparent compaction rate, apparent cementation rate, apparent dissolution rate, and apparent micropore rate parameters. The comprehensive coefficient of diagenesis was selected to act as the quantitative characterization parameter of diagenetic strength and diagenesis combination, and it exhibits good statistical correlation with displacement pressure, soring coefficient, reservoir quality index (RQI) and fractal dimension. Different pore structure types have different diagenesis combination characteristics and comprehensive coefficients of diagenesis. The comprehensive coefficients of diagenesis can be regarded as the quantitative characterization parameters of different pore structure types. Based on diagenetic types and thorough analysis of impact on pore structure characteristics, the qualitative division and quantitative evaluation can be implemented through comprehensive coefficients of diagenesis.