In view of the problem of the projection distortion and precision requirement when establishing horizontal control network of large area and high altitude project,this paper analyzes and discusses the projection distortion and elevation projection plane based on the Lancang-Mekong River channel project.Finally we select the method of arbitrary zone Gauss-Krueger projection with elevation projection plane,and adopt the multiple projection zones and multiple projection planes scheme to establish the coordinate system.It is proved that this coordinate system can effectively solve the problem of projection deformation and meet the requirements of project precision,provide a technical reference for similar large-span and large-height surveying and mapping projects.