Through researching on diagenesis of Chang 8 reservoir sandstone in the Heshui region of Ordos Basin, it could find the reasons of low permeability and porosity, and fulfill prospect and evaluation of those zones where the high quality reservoirs are developed. Based on the sedimentary facies research, using the microscope and the scanning electronic microscope, it is analyzed at diagenetic microscopic feature. The sandstones of Chang 8 sandstone is divided into six diagenetic lithofacies: mica intensive compaction, carbonate cement facies, feldspathic solution facies, kaolinite cement facies, chlorite remnant intergranular pore facies, chlorite remnant intergranular pore-feldspathic solution facies.