Abstract: A scientific classification scheme of rocks is the basis for study of fine-grained sedimentary rocks. Based on analysis of the mineral components of fine-grained sedimentary rock from Guan-X Well drilled on the second member of Kongdian Formation in Cangdong Depression, this paper comes up with the scheme for classification of fine-grained sedimentary rocks on the basis of X-ray diffraction data. This scheme is a three-unit four-component division system. The three units are carbonate minerals, clay minerals and felsic minerals. Finegrained sedimentary rocks are divided into 12 types of rock in four main categories, such as fine-grained felsic sedimentary rock, carbonate rock, clay and fine-grained mixed sedimentary rock. Meanwhile, with analcime taken as the fourth component, fine-grained sedimentary rocks are named according to the concrete content of analcime. This scheme can unify the classification system of fine-grained sedimentary rocks and promote unconventional hydrocarbon exploration and development in the fine-grained facies zones.