This paper combines the climatic,hydrological and geological conditions of Yuanxi Expressway subgrade construction,takes the three different admixtures of slag powder,fly ash and mineral powder in tunnel construction as examples,combines the characteristics of project construction,and carries out orthogonal combination of concrete according to different blending ratios.Through testing and processing the results of slump,expansion,compressive strength and electrical flux of the concrete added with the mixed admixtures,the optimal blending ratio of slag powder,fly ash and mineral powder is determined.It has very good reference significance for other similar projects.