Chloritization is a typical hydrothermal alteration type of early ore-forming stage in Shulouqiu deposit of Changjiang rock mass in southern Zhuguang. In this paper, the altered mineral-chlorite in the horizontal alteration zone around the ore body are studied comprehensively by optical microscopy, electron probe and scanning electron microscopy. They are divided into five types: fissure filling chlorite, biotite altered chlorite, feldspar altered chlorite, dolomite altered chlorite and spherical chlorite, by mineralogical characteristics and origin of chlorite. The five types of chlorite are all trioctahedral iron-rich chlorite with the same structure type, belonging to three species: vermicular chlorite, ferromagnesian chlorite and uraninite chlorite. Then, the five types of chlorite may have formed in the same period of fluid action in the early ore-forming period, with the formation temperature between 219~282°C and LogfO2 between -43.35~-47.74. Combined with previous research results in the region, the early ore-forming fluid may be a crust-mantle mixed fluid dominated by mantle-derived materials, with strong reducibility. Its formation is related to the intrusion of regional basic veins, which provides a reducing field for the mineralization system, resulting in the reduction and precipitation of U6+ in the ore-forming fluid.