Abstract: The co-precipitate of Thorium and Uranium（AUTh C） was prepared by co-precipitation technique, the（Th,U）O₂+x powder was obtained by the decomposition and reduction of the AUTh C. The decomposition process of AUTh C was analyze by DTA-TG, the specific surface area of（Th,U）O₂+x powder was measured by BET method. The parameters which may effect the（Th,U）O₂+x powder properties were investigated, such as p H value, ammonia and ethanol. The result shows that the precipitation ratio was higher when the p H value was 5.5. Adding ammonia to make the p H value exceed 7.5 could improve the co-precipitation process. In the filtrate, the concentration of Uranium was 86 mg/L, the concentration of Thorium was 105 mg/L. Ethanol can prevent（Th,U）O₂+x powder grows hard-agglomeration in decomposition process, and the specific surface area of（Th,U）O₂+x could get up to 15 m²/g on the condition that the AUTh C decomposed at 600℃ for 2 h.