Abstract: The effect of calcium-uranyl-carbonate complex on the adsorption of uranium on red soil was investigated through static adsorption experiment. The results indicate that the increases of pH and concentrations of dissolved carbonate and calcium ion can suppress U(Ⅵ) adsorption on red soil. When pH is 7.0, dosage of red soil is 1 g/L and concentrations of calcium ion, dissolved carbonate and uranium are 0.4 mmol/L, 3.8 mmol/L and 50 mg/L respectively, the maximum adsorption capacity is about 4.20 mg/g. The uranium is mainly adsorbed in the forms of UO₂(CO₃)^2-₂, UO₂(CO₃)^4-₃ and UO₂CO₃(aq). The c(U-CO₃)_T can be used to predict uranium adsorption capacity of red soil. The c(U-CO₃)_T has a nonlinear relationship with q_e, and the equation is q_e=18.2(c(UO²⁺₂) c(CO^2-₃) (K₁+K₂c(CO^2-₃)+K₃c²(CO^2-₃)))^0.36. The research results can provide technical or theoretical references for uranium contaminated red soil remediation.