Taking a mountain tunnel as example, the article makes investigations on and measurement of the cracks of the tunnel linings and makes analysis on the causes for the cracks and on the impact degree of the cracks on the tunnel structures. Then the article expatiates on the technical process and construction methods of the treatment of the cracks and seepage water in terms of cracks without water and cracks containing water. Finally, the article makes some recommendations on the prevention of the tunnel lining cracks.