The quantitative determination of pore throat structure and diagenetic effects are of great prospect value for exploration and development. Starting from the petrology characteristics, 34 core samples of Chang 4 + 5 oil formation were obtained from 13 different data wells in Zhenjing area. The micro-pore throat structure of Chang 4 + 5 oil formation was studied by core displacement test, cast thin section analysis, mercury injection analysis and test. The results show that the sedimentary environment of the Triassic Chang 4 + 5 oil formation in Zhenjing area is in middle diagenetic stage. In the whole sedimentary process, it is mainly caused by the mechanical compaction in early stage, and the secondary quartz expansion in the stage, also cementations and fillings caused by the diagenetic autogenetic mineral precipitation, the dissolution of feldspar, rock debris and the formation of micro-fractures in middle stage. Secondary pores are generated, which provide favorable storage space and circulation channel for hydrocarbon accumulation and charging.