Mapping contour lines requires a large number of elevation points data and it’s very difficult to survey the area with vegetation cover.Considering the disadvantages mentioned above, the large scale mapping method was put forward by fusing the contour lines of small scale topographic maps and feature points with CASS mapping software.The mountain area of Xiangtan county,already having its small scale mapping,was chosen as the experimental area.The large scale contour line was adjusted by surveying some elevation data and using the small scale mapping. The precision of fused contour lines were compared and analyzed the practical value of producing large scale mapping by this way.It proves to be reducing the labor intensity and raising the measuring efficiency and it is a practical and efficient large scale mapping method.