Abstract: The study area is located in Risong villages of Tibet. In order to provide the basis for Mesozoic stratigraphic age in this area, lithology combination, sedimentary environment, paleontological characteristics were studied. A lot of Early Cretaceous index fossils, such as Orbitolina (Palorbitolina)complanata and Stylina parvistella Volz, were found in the Jurassic strata in the 1:250 000 geological survey in Ritu County. These fossils provided strong evidence of the division of stratigraphic age in this area. Combining with analysis of sedimentary environment, the conclusion can be made that sedimentary facies in early Cretaceous of this area developed in residual sea basins.