Fusui bauxite deposit is a typical Karst bauxite deposit, which is found in southwest of Guangxi Province. Based on the field survey, by the means of microscope, X-ray diffraction, hydrogen and oxygen isotope testing, the mineral intergrowth and H, O sotopes date were analyzed, and the changes of metallogenic environment and the genesis of diaspore were discussed. XRD and microscope observations show that the diaspore and kaolinite are the main minerals, and boehmite, hematite and anatase are the subordinate minerals. Chlorite and pyrite form during deposition stage. Pyrophyllite and illite form during post sedimentary stage. Boehmite is not obtained in accumulative bauxite. H, O isotopes data show that delta~(18)O of diaspore is at range of 0.95%-1.98%, and deltaD is between -6.5% and -7.94%; kaolinite delta~(18)O is 1.3%-1.89%, and deltaD is -7.04%- -8.97%. Mineral association indicates that the bauxite is deposited in anoxic environment, which experiences the oxidizing environment and alternation of arid and wet climates during post sedimentary stage. H-O isotopes composition of diaspore is coordinated with terra rossa, and have the characteristics of weathering crust and laterite, which indicates Fusui bauxite is transformed by terra rossa. H-O isotopes composition of kaolinite shows the temperatures of 33 ℃ in deposition and 18 ℃ in post deposition, which approximate sea water from the Late Permian to middle triassic. In conclusion, the transformation of gibbsite and boehmite to diaspore is related to the volcanic activity caused by subduction of the Tethys sea. The formation of the primary sedimentary bauxite is a response to global climate change in the Permian-Triassic. The formation of diaspore in accumulation ores are related to the indosinian movement and karstification.