The carbon and oxygen isotopic compositions of calcite cements in the host strata of sandstone type uranium deposit have important theoretical and practical significance for the study of metallogenic mechanism. The predecessors have done a lot of research work on the qualitative judgment of the source of ore- forming fluid, but the quantitative understanding of the component characteristics and related parameters of ore- forming mixed fluid is still lacking.Methods: The carbon and oxygen isotopic compositions of calcite cements in different sandstones inZhiluo Formation in Zaohuohao uranium deposit in southeastern Dongsheng area were analyzed, and the carbon and oxygen isotopic compositions of calcite cements in Zhiluo Formation in Zaohuohao uranium deposit and Nalinggou uranium deposit in northwestern Dongsheng area were studied.Results: A quantitative genetic model of carbon and oxygen isotopic compositions of calcite cements produced by the mixing of two different fluids between the seeping hot brine and the seeping formation water was established, and the comprehensive factors such as the source of the two fluids, the concentration ratio of dissolved carbon, the proportion of the fluids and the temperature of the hydrothermal solution were studied.Conclusions: Except for a few calcite cements formed during stratum deposition, most calcite cements precipitated as a result of mixing of hot brine and formation water. Decarboxylation of Paleozoic organic acids resulted in CO2 enrichment in hot brine. The ratio of formation water of ore- forming fluid to hot brine in sandstone type uranium deposit in Dongsheng area is 0.5 to 0.9, and the ratio of formation water is more than two- thirds; the ratio of dissolved carbon in hot brine to formation water is mainly in the range of 1.5 to 5.0, and some of them are more than 10.0; the concentration of dissolved carbon in hot brine is high which the fluid is enrichment in CO2. The mixed fluid temperature can be divided into two main ranges of 55℃to 80℃ and 90℃ to 140℃. Combined with the inversion of paleosalinity and salinity index, it shows that the ore- forming fluid is a low- temperature hydrothermal mixed fluid of organic and inorganic origin. The carbon and oxygen isotopic compositions of calcite cements in sandstone type uranium deposits can be used to quantitatively simulate the ore- forming conditions of the two fluids, such as the ratio of dissolved carbon concentration, the ratio of the two fluids and the temperature of calcite formation, so as to explain the genesis of carbonate cements and better understand the ore- forming process from the perspective of ore- forming fluids.