Hailaer Basin is one of the areas with great prospecting potential for in-situ leachable sandstone-type uranium deposits found in recent years. At present, good uranium mineralization has been found in the Kelulun Sag in the southwest of Hailaer Basin, and the ore-bearing target layer is the Lower Cretaceous Yimin Formation. Scanning electron microscopy, X-ray diffraction and electron probe analysis were used to study the relative content of clay minerals, microscopic characteristics and occurrence forms of uranium minerals in the sandstone of Yimin Formation in the study area. The results show that the clay minerals in the Kelulun Sag are mainly chlorite, followed by kaolin, montmorillonite and illite-montmorillonite mixed layer. Uranium mainly exists in the form of uranium stone, followed by adsorbed uranium and a small amount of pitchblende. Montmorillonite, kaolinite and chlorite in the study area have mutual conversion phenomenon. Under alkaline conditions, when Ca²⁺, Mg²⁺ and Na⁺ exist, some montmorillonite is converted to chlorite. When Fe²⁺ and Mg²⁺ exist, some kaolinite is converted to chlorite. The alteration of clay minerals provides a local alkaline environment for the formation of uranium in the study area.