Abstract: he 500kV Direct Transmission Line is across the entire Qinghai-Tibet plateau. So its environment has a tight link with frozen soils. Because of freezing soil specialty of frost-heaving and thaw-settlement, the transmission line would meet the great challenge in survey, design, construction and operation in post-construction stage. Therefore, in order to learn more about permafrost engineering problems of transmission line, the physical and mechanical tests are conducted. This paper analyzes the influence factors on the tower stability. The test results show that freezing and thawing behavior can increase the sensitivity as the water content increases for the same soil samples. If the water content keeps the same, the freezing and thawing behavior increases the sensitivity as the particle size decreases for different soil samples. Also, the results show that the geological environment, harmful features of frozen ground, different geomorphic units, thermal stability characteristics of permafrost, and the convenient construction are the factors influencing the tower foundation stability.