Thaw lake is a common landscape in permafrost regions. The presence of a water body thus constitutes a heat source and releases the heat energy to the permafrost beneath and around lake, giving rise to the ground temperature increase. A talik, even penetrated talik maybe occur under the lake-bottom. The decline of permafrost table, elevation of permafrost base on the lakeshore accelerates the rapid permafrost degradation. This study predicted the temperature changes beneath and around lake and the process of permafrost degradation. The results showed that when the water depth is 2 m and 4℃ of mean annual lake-bottom temperature, the increase of ground temperature is about 4.7-3.2℃ beneath the lake-bottom, 2.2-1.1℃ beneath the lake-edge, and 0.3-0.1℃ beneath the lakeshore after 1000a. When the mean annual lake bottom temperature equals to or is less 0℃, a talik is impossible formation under the thaw lake; if the temperature increases to 1℃, a 25 m deep talik forms after 500a and the permafrost will be thawed completely after 900a. Therefore, the time of permafrost disappearance shortens with the increase of mean annual lake-bottom temperature.