Abstract: Hydrogen reduction method has been widely studied and applied in the hydrometallurgy preparation of metal powders or oxides due to its simple operation, clean and environmental protection. A large number of research reports have emerged in the metallurgical processes and technologies of platinum group metals, nickel, cobalt, copper, vanadium and other metals. If the hexavalent uranyl ions in the solution are reduced to tetravalent by hydrogen reduction method, it is expected to achieve selective reduction and precipitation of uranium and produce high-quality uranium oxide products. However, the existence of uranium in alkaline solution is complex and changeable, with multiple valence states and hydrolysate products, and it is difficult to obtain the ideal hydroreduction effect without systematic research on the thermodynamics of hydroreduction precipitation of uranium. The potential-pH diagram is a phase diagram drawn according to the function relationship between the equilibrium potential of various reactions in the system and the pH value of the solution, which can be used to judge the possibility of the reaction under the system, the stability of the product, determine the chemical equilibrium conditions in the solution, the direction of the reaction and the dominant area and range of a certain component, provide a thermodynamic basis for the chemical reaction of the solution, and also carry out theoretical analysis, improvement and perfection of the production process. In order to determine the thermodynamic properties and influencing factors of uranyl carbonate hydroreduction, the potential-pH diagram of the U- \mathrmC\mathrmO_3^2- -H₂O system was drawn by thermodynamic calculation, and its influencing factors were discussed. The diagram analyses show that under the U- \mathrmC\mathrmO_3^2- -H₂O system, the reduction of uranium from hexavalent uranyl carbonate ions to tetravalent uranium dioxide precipitate is thermodynamically feasible, and the dominant area of uranium dioxide is large, and there are basically no other forms of uranium compounds. Although the reaction temperature and solution carbonate concentration have a certain effect on the reduction potential of hexavalent uranium, they do not affect the reduction of hydrogen and the formation of uranium dioxide precipitation as a whole. The hydroreduction verification test was carried out using the alkaline uranium qualified liquid obtained from a leaching mine, and the test results were consistent with the thermodynamic analysis results. The potential-pH map of this study can be used to guide the experimental research and industrial practice of uranium products prepared by hydroreduction of uranyl carbonate solution, which provides a new technical support for uranium mines to directly prepare high-quality uranium oxide products from alkaline uranyl carbonate qualified liquid.