Abstract: Based on the data of core, cast thin section, SEM, clay mineral analysis by X-ray diffraction and physical property analysis, the paper analyzes the forming mechanism of authigenic chlorite and its influence on reservoir physical properties of the conglomerates in the Lower Triassic Baikouquan formation in Xiazijie fan and Huangyangquan fan of Mahu sag. The study results show that the authigenic chlorite in the conglomerates occurs mainly in 3 types such as grain-coating, pore-lining and pore-filling. The authigenic chlorite was mainly developed in alkaline water environment with high Fe2+ and Mg2+ content and originated from clay mineral transformation, volcanic material alteration and pore water crystallization. The gravels with grain-coating chlorite developed are in point and line contacts, which could improve the ability to resist compaction and mechanical strength of the rocks. The development of pore-lining chlorite restrains the growth of quartz. The authigenic chlorite is in favor of pore preservation in reservoirs. The effective porosity of the conglomerate reservoirs in Baikouquan formation of Mahu sag increases with the increase of the content of authigenic chlorite, and the higher the content of authigenic chlorite, the better the oil bearing property of the reservoir will be