The Great Wall is not only the symbol of the ancient Chinese culture but also an actural and significant geographic boundary. The arrangements of the wall in past dynasties are based on physiographic conditions, and are Just Consistent with the demarcation line between semi-humid and arid climates in the country. Therefore, the Great Wall becomes an indicator of the demarcation line between the two areas. The extension and retreat of the wall generally reflect the expansion and shrinkage of farming and animal husbandary areas. From the viewpoint of political geography, the Great Wall can be regarded as the balance belt of "forces" where the political powers of different nationalities historically stood facing each other and had repeated trials of strength.On one hand, the man-made wall of 10000 Li had the function of separating two political units; to some extent, the extension and retreat of the wall reflect the changes of relative strength of the two sides. On the other hand, the conflicts of the advanced and backward forces objectively promoted the economic and cultural exchanges as well as the national assimilation. Today, the Great Wall had lost its function of military works for territiry expansion and defence, but it is still the significant indicator as a geographic boundary and a sensitive area for many geographic elements.