Abstract: Clay mineral is an important part of cement in clastic rock reservoir and its type and content have great influence on the quality of the reservoir. Based on the research of thin section, cathodoluminescence, mercury intrusion data, SEM, X-ray diffraction, physical properties and other data, the authors analyzed the clay minerals in Weixinan Sag and Wenchang A Sag. The results show that the dessert reservoir is closely related to the clay mineral, and two clay mineral assemblages of relatively high-quality reservoir are developed in low permeability background. The dessert reservoir of Liushagang Formation in Weixinan Sag are mostly developed in medium coarse sandstone and gravel bearing coarse sandstone. The activity of acid fluid and dissolution in the reservoir is strong. The relative content of kaolinite is high, and the pore types are mainly dissolution pores and intergranular pores. There are two genesis kinds of kaolinite, which are the leaching of atmospheric fresh water and dissolution of organic acid respectively. The high-quality reservoir of Zhuhai Formation in Wenchang A Sag is mainly located in the front of fan delta, and the deposit is transformed by paroxysmal water flow and sea water. The relative content of chlorite is high, and the pore type is mainly residual intergranular pore. The main types of chlorite are granular coating and pore lining, supplemented by cluster chlorite filled between grains. The analysis of the relationship between clay mineral and dessert reservoir is of great significance to the dessert finding and oil and gas exploration.