Abstract: With the further improvement of the research and development requirements of special nuclear reaction devices, the existing sodium and sodium-potassium alloy coolant system can’t meet the requirements of high-temperature operation, the lithium cooling scheme has gradually become the research object of scholars at home and abroad, among which the purification and detection of coolant impurities are the prerequisites for the research and operation of lithium cooling reactors and other high-temperature lithium circuit systems. Nonmetallic impurity oxygen is the most common and harmful substance in lithium, once the oxygen content is too high, it will cause material embrittlement and produce solid oxides, which will cause flow blockage, endanger the safety of the circuit, and even lead to reactor safety accidents. Therefore, in the high-temperature lithium circuit system, the oxygen impurities in lithium must be strictly monitored and purified. The electrochemical oxygen meter is an effective technology for real-time detection of oxygen content. In this paper, based on the research and development experience of sodium-electrochemical oxygen meter. The coexisting phase Bi/Bi₂O₃ with stable high-temperature output potential, weak temperature sensitivity and relatively mature manufacturing process was selected as the reference electrode, 3%Y₂O₃ with good conductivity was selected as the solid electrolyte, they form a primary battery structure together with lithium liquid. The calculation model of lithium-electrochemical oxygen meter was established based on thermodynamic reactions and Nernst equation. The theoretical oxygen potential relationship was obtained, and an electrochemical oxygen meter prototype was developed. Preliminary tests such as start-up characteristics and calibration were completed on the lithium circuit. The results show that the electrochemical oxygen meter has an activation temperature, and the output potential has a good follow-up with the temperature after exceeding the activation temperature. In the calibration oxygen concentration test, the output potential has a certain deviation from the theoretical value, but the overall change trend is consistent. After fitting the formula, the relative deviation between the calculated value and the measured data is not more than 1%.