Abstract: This paper analyzes the main influences of environmental conditions on the constructions of the Qinghai-Tibet railway.The conditions are the instincts of temperature,moisture,and environment of permafrost..Then the features of the interactions between tthe engineering environment and the permafrost conditions in the permafrost region are discussed.Finally it is concluded that the key problem to ensure the engineering safety reliability in permafrost region is to control the heat erosion from external environment to the system of permafrost engineering environment.