Loh rapids on the Lancang-Mekong River has the characteristics of curved,shallow,risks,narrow and rapids.Based on analysis of the site investigation data and results of the mathematic model calculation,this paper analyzes the causes of the rapids and the characteristics of the navigation.The rocks and cobblestones,which rushed out from Nile River by torrential flood,accumulate in estuary of the river and form an alluvial fan.In recent years,because of the development of the alluvial fan,river drainage section is occupied.Furthermore,the coastline is uneven.All those cause the water bend at the top of the rapids,and steep in the middle.It is difficult for ships to pass through rapids.In view of the causes and characteristics of Loh rapids,this paper puts forward the measures to combine the reefs and regulating structure in order to solve the problem of navigation.