Factors which control the variation of permafrost table along the Qinghai-Tibet Highway were analyzed based on date of the active layers, borehole's ground temperatures and hydrothermal observation. It is found that the permafrost table along the Qinghai-Tibet Highway has a decreasing tendency overall, consistent with the regional tendency  climate change of recent years. Permafrost table has declined by 0.1-0.5 m dependent on geographical position. Air temperature change is one of the significant external factors which control the permafrost table. The extent of change of permafrost table is also limited by geographical environment and soil internal structures. The study of permafrost table changes aims to turning its control condition from natural to artificial, which is very important for engineering constructions.