Abstract：Paleogene and Neogene lacustrine carbonate rocks are widely outcropped in the western Qaidam Basin. They are mainly distributed in Xiaganchaigou Formation, the top of Shangganchaigou Formation, Xiayoushashan Formation, the bottom of Shangyoushashan formation in Xichagou area. Based on the measured section, lithologic analysis, lithofacies assemblages, biological characteristics, sedimentary structures and thin section identification, the authors analyzed carbonate rocks of Xichagou section. The results show that the types of carbonate rocks are mainly oolitic limestone, shell limestone, algal-stromatolite limestone, micritic limestone and arenaceous limestone, with the depositional environment being mainly littoral and shallow lake. The genesis of the carbonate rocks are also analyzed on the basis of petrology.