<p>The complexity of diagenesis and its evolutionary processes in the Chang 2 reservoir complicates the identification of high-quality reservoirs, thereby directly affecting reservoir evaluation and subsequent oilfield development decisions. The diagenesis process and pore evolution of Chang 2 reservoir in the Caoduowan area in the Ordos Basin were analyzed by using the methods of cast thin section, grain size analysis, mercury intrusion porosimetry, cathodoluminescence, X-ray diffraction (XRD) and fluid inclusion analysis. The findings indicate that the Chang 2 reservoir is predominated by feldspar sandstone, which primarily develops dissolution pores, intergranular pores and micro-fractures. Diagenetic modifications, including compaction, cementation, and dissolution, have collectively controlled the porosity evolution of the Chang 2 reservoir. In light of the disparity in diagenesis, the reservoir can be categorized as the chlorite-cemented intergranular pore type, the feldspar-dissolution intergranular pore type, and the carbonate-cemented composite pore type. The feldspar-dissolution intergranular pore type reservoir underwent strong compaction at an early stage, but the significant dissolution effect resulted in better reservoir physical properties. The chlorite-cemented intergranular pore type and the carbonate-cemented composite pore type reservoirs exhibit relatively fine intergranular porosity during the early and middle diagenetic stages. Nevertheless, the carbonate-cemented composite porosity reservoirs are impacted by late cements, leading to the deterioration of their physical properties. By quantitatively characterizing the diagenetic evolution of three representative reservoir types, this study clarifies the controlling factors for the development of high-quality reservoirs. These results provide a geological basis for predicting favorable reservoir intervals and guiding development adjustments in the Caoduowan area.</p>