Channel is the reason resulting in water seepage from Kunlun Mountain tunnel by analyzing relationship between location of seepage and terrain. Moving boundary is redefined to rediscovery permafrost; and the essential conditions resulting in moving boundary are presented too. A computational model of moving boundary is introduced to compute thawed depth of permafrost; and how to determine some parameters is discussed. The computational results are compared with the actual ones. The disciplinarian of variation of frozen-thaw range around Kunlun Mountain tunnel is drawn to treat disease of the tunnel finally.