Abstract:CO2+O2 in-situ leaching of uranium process is the third generation of uranium mining and metallurgical technology in China, during the in-situ leaching process, the dissolved liquid reacts with the ore-bearing seam minerals to extract uranium from the ore, at the same time, chemical precipitation will occur due to the increase of groundwater mineralization, resulting in ore-bearing seam blockage. CaCO3 precipitation is an important cause of ore layer blockage during in uranium leaching in CO2+O2. In order to explore the conditions of CaCO3 precipitation and blockage, hydrogeochemical conditions of ore-bearing seam blockage were systematically studied through hydrogeochemical simulation, according to the chemical composition data of CO2+O2 uranium leaching solution from uranium ore in Nalinggou in Inner Mongolia The results show that CaCO3 precipitation is the important cause of chemical blockage of ore-bearing seams in CO2+O2 in-situ leaching of uranium. When the pH value of the leaching solution 6.5 above, CaCO3 will precipitate, the pH value, concentration of HCO3- and Ca2+ of the immersion solution are the main factors affecting CaCO3 precipitation, and excessive pH value and concentration of HCO3- and Ca2+ will cause the production of CaCO3 precipitation. According to the simulation results, the relationship between pH value, and concentrations of HCO3- and Ca2+ without CaCO3 precipitation is obtained, and it is concluded that maintaining the lower Ca2+ concentration and lower pH value of the leaching solution is an effective way to prevent and alleviate CaCO3 precipitation blockage.