Cross-border water resources cooperation is of great significance to the construction of a community of shared future for Lancang-Mekong countries. International cooperation is an inevitable choice to solve the current problems of cross-border water resources cooperation. Due to the complexity of international hard law formulation and the uncertainty of implementation effect, cross-border water resources cooperation in the Lancang-Mekong River Basin can be carried out from the perspective of international soft law. The Lancang-Mekong water resources cooperation mechanism has made a series of achievements in mechanism construction, information sharing, scientific, technological and cultural exchanges, but it still needs to be improved by establishing joint management institutions, expanding its influence, encouraging the joint participation of basin countries, and increasing the types of cooperation subjects, so as to accelerate the pace of building a community of shared future for Lancang-Mekong countries and promote the economic and social development of Lancang-Mekong countries.