Abstract: Based on the data analysis of casting lamella,scan lectron microscope and X-ray diffractions etc,the diagenesis is belong to the"B"middle diagenesis on the Chang 6 reservoirs in Baibao area of the Ordos Basin.The compaction and carbonate-cementation destroy the primary-texture of pore intensively,which deteriorate the physical property.The cementation of clay minerals improve the pore for growth of chlorite,but will deteriorate the permeability since they jamed the throat.Dissolution and fracturing change the pore structure effectively,which improved the physical property of reservoirs.