Abstract: The dominant of clay minerals in sandstone within the area were anthigenic kaolinite,chlorite and illite-smectite,but illite-smectite,kaolinite,less chlorite in mudstone.Transformation of clay minerals in sandstone and mudstone had similar condition of water-bearing medium and earth's temperature,and closely related to hydrocarbon generation and migration.It is indicated that the authigenic clay minerals in sandstone and mudstone were both formed in middle-late diagenesis age.The transformation and dehydration of clay minerals in mudst one provided fluid and dissolution matter for sandst one.The decarboxy lation of organic matter in mudst one provided fluid and acid-water for sandst one,so facilitated the dissolution of detrital grains in sandstone and the generat ion of second porosity.