Abstract: The examination of petrology,diagenesis,porosity type and evolution indicates that the Chang-2 reservoirs composed of feldspar sandstone and lithic feldspar sandstone with low compositional and textural maturity have undergone several stages of diagenesis including compaction,cementation,replacement and dissolution.The Chang-2 reservoirs in the Pengtan-Yangjing region,Ordos Basin are now in Stage A of the late diagenesis judged from diagenetic characteristics,burial depth,palaeo-geotemperatures and organic matter maturity.