The invention relates to a triangular elevation measuring method applied in highways in mountain areas. A total station is erected at a place inter-visible to two prisms by using two total stations bymeans of a free station method; the height difference between an observation station and the two prisms is observed, and a round-trip measurement height difference between a starting point and an endpoint of a measuring section is measured indirectly; and bilateral observation is adopted, the height difference between A and B is an average value of the height difference measured by the two totalstations, and the height difference is obtained through calculation. According to the above analysis, a method of simultaneous bilateral indirect height difference observation method by a measuring robot and double observation stations is adopted, so that the influences of atmospheric refraction and the earth curvature are eliminated. Theoretical analysis and practice prove that the method can achieve the precision of the third-class leveling, and the measurement efficiency is much higher than that of the traditional level.