Abstract: Thaw slumping existing on two slopes in the permafrost region of Qinghai-Tibet Plateau are studied with their geological, frozen soil conditions and deformations. The extending area, the sliding velocity and the water content of soil strikingly change with the air temperature and slope aspect. The dominant causing factors of this kind of slope instability are ice-rich frozen soil and slope-cut. Engineering measures should be based on principle of protecting permafrost, and attention should be paid to ground water drainage too.