The multi-fractal spectrum of natural surfaces was computed and analyzed with the multi-fractal method. The parameters of multi-fractal spectrum were used to describe hierarchically refined structure of terrain and pop out the singularity characters of local area. Thus, the exact characterization of terrain surfaces obtained, the areas that have distinct thumbprint can be selected from complicated terrain. Combining multi-fractal spectrum parameters with the fractal dimension of single fractal, the terrain areas can be classified, and selection of flight path can be done. The results of experiment show that multi-fractal spectrum function is effective and better than single fractal in acquiring terrain character information, the difficulty in classing of terrain when the fractal dimensions are nearly same is solved. Multi-fractal spectrum is more fit for description of complexity and fluctuation of terrain, and can be used effectively in navigation and flight path programming.