Kunlunshan tunnel on QinghaiTibet railwayis located on the west of Luanshigou at the north foot of Kunlunshan Mountain, which, with over 4000m absolute elevation, belongsto permafrost region. Kunlunshan tunnel, with a total length of 1686m, is so far the longest permafrost tunnel in the world. The tunnel was completed in September, 2003. Since Kunlunshan tunnel penetrates through permafrost ground, a series of countermeasures are taken, which include the key measure of water blockingand otherassociated measures such aswaterproofing, water cuttingoff, drainage, thermal insulation and temperature keeping, so as to minimize the heat exchanges between the inner side and outerside of thetunnel lining and to keep the water contained in the rock mass in frozen state after tunnel breakthrough. Therefore, the design and constructionofwaterproofingand drainage of permafrosttunnels have their own particularityand areimportant technological problems to be solved. On basis of engineering practices, in the paperthe author presents the design and construction of the waterproofing and drainage of Kunlunshan tunnel.