Research conclusions：(1) From the monitored data in recent years, it can be seen that the long-term monitoring system for Qinghai-Tibet Railway has worked well. The monitored data are true and reliable. They can be as the basis for evaluation of the stability of engineering structure in permafrost area along Qinghai-Tibet Railway. (2) The long-term monitoring system has continuously monitored the subgrade in permafrost area for many years and found out the environment characteristics and settlement mechanism of the subgrade in permafrost area when the subgrade occurred big settlement and deformation. Based on them, the strengthened measures will be presented to better maintain the subgrade, improve the water thermal condition for the subgrade system, relax the drop of manual upper limit and slow down the settlement rate of the subgrade. (3) From the analysis of the monitored data on the bridge and the cross-section of culvert in permafrost area, it is believed the foundations of the bridges and culverts are entirely stable.