Ruoergai uranium deposit is one of the four basic types of uranium ore fields in China, the formations are limestone and silicon limestone with the development of groups longitudinal fissures. There was no mud return while drilling in such kind of formation because of the total lost circulation. It was very difficult to maintain mud properties and borehole stability and a lot of manpower and material resources were spent on this. Based on the analysis on the mechanism of lost circulation, a technical measure was put forward. The basic idea is to reduce leakage pressure for balanced drilling. The research and experiments were carried out on air bubbles mud, micro-bubble mud and cenospheres mud systems. The practice shows that the cenospheres low-density mud system is suitable for drilling operation in Ruoergai uranium ore field.