Based on methods of rock thin section identification, fluid inclusion uniform temperature test, burial history and organic matter thermal history analysis, gypsum bed dehydration and clay mineral transformation analysis, it was shown that reservoirs in the Member 4 of the Shahejie Formation in Hexiwu structural zone had experienced alkaline→acidic→alkaline→weak acidic→weak alkaline diagenetic environment during their evolution process. Moreover, the diagenetic evolution sequences were compaction→feldspar dissolution and/or secondary enlargement of the quartz→carbonate cementation and/or anhydrite cementation→little carbonate cement dissolution→little pyrite cementation. According to the principle of inversion and back-stripping, the authors calculated each of the key diagenetic contributions on reservoir plane porosity quantitatively on the basis of casting thin sections with different diagenetic characteristics in the study area. Furthermore, the actural porosity was calculated by using the functional relationship with porosity. Finally, the evolution histories of actual porosity with different diagenetic characteristics have been established quantitatively combined with the mechanical compaction correction. In summary, from the matching relationship between porosity evolution and hydrocarbon accumulation period, in the first period of hydrocarbon accumulation, the reservoir physical properties were good with porosity up to about 20％. In the second period of hydrocarbon accumulation, the reservoir porosity rapidly decreased to about 7％ in the northern block as a result of intense carbonate cementation, and was not good for hydrocarbon accumulation. However, carbonate cementation in the southern block was weak, and most of the reservoir porosity is bigger than 10％. Therefore, the southern block was good for hydrocarbon accumulation, and became the favorable exploration target.