ABSTRACT:   Water is an important resource in “the Belt and Road Initiative”. As the most important transboundary river in Asia, the Lancang-Mekong River plays a significant role in the development of aquatic ecosystems in “the Belt and Road Initiative”. For this reason, in this paper, non-radial direction distance function is used to analyze the water use efficiency of the Lancang-Mekong River Basin region from two perspectives (total-factor and water-factor indicators). Then, the influencing factors of water use efficiency in the Lancang-Mekong River are discussed using gray correlation analysis. The result shows that water use efficiency of Thailand, Cambodia, Yunnan and Qinghai is at a relatively optimal level, whereas for Vietnam, Tibet, Laos and Myanmar, it is relatively low. Economic development level, technological progress, industrial structure and trade and foreign investment have an impact on water use efficiency. Among the influencing factors, economic development level has the greatest impact.