The diagenesis and pore evolution of Yan 25 and Zhuang 40 areas in the Ordos basin were analyzed.The research shows that the sandstone layers of the two areas are currently at the second stage of the middle-diagenesis period and controlled by acidity and alkalinity of diagenetic environment.Sloanite and chlorite are very developed within the Chang 6 Formation of Yan 25 area,and solution pores of sloanite are the favorable place for gas/oil reservoir;whereas kaolinite is widely spread in the Chang 6 Formation and the main reservoir in Zhang 40 area is the feldspar and debris solution pores.The quantitative study of pore evolution shows that the pore evolution differs even at similar diagenetic stages.The primary porosity is similar:34.91% for Yan 25 and 33.42% for Zhuang 40.During mechanic compaction,the loss rate of porosity in Yan 25 is 40.33% and Zhuang 40 is 55.45%.During cementation and metasomasis,the loss rate of Yan 25 is 46.86%,and that of Zhuang 40 is 36.51%.The secondary porosity is mainly sloanite solution pores in Yan 25 area and feldspar and debris solution pore in Zhuang 40 area.The proportion of secondary porosity takes up to 55.76% in Yan 25 and 73.51% in Zhuang 40.Therefore,the quantitative analysis of porosity evolution in sedimentation-diagenesis provides a good reference for the sieving of high-quality reservoir and progressive exploration.