To deeply study the treatment method for instability of highway cutting slope under the condition of expansive soil overlying rock layer in an alpine region，the comprehensive treatment method of unstable slope under this bad geology was put forward based on the unstable slope project of Zhangbei?Shangyi Expressway.The governance protection structure consisted of a rigid protection system，drainage system，thermal insulation system，flexible protection system，and waterproof system.The rigid protection system was an anti-slide pile setting at the height of 1/3 of the first grade slope，of which parameters were calculated by cutting the slope of the rock layer in the unstable area to reduce the required anti-slide force of the remaining soil.The drainage system consisted of built-in tilting drainage pipes between the rock layer and expansive soil layer，gravel drainage layer outside the expansive soil layer after excavation of soil in unstable area，horizontal drainage pipe in the gravel layer，drainage ditch，intercepting ditch and side ditch of each platform.The thermal insulation system was a backfill soil layer and a cultivated clay layer arranged outside the gravel layer.The flexible protection system was a geogrid in the thermal insulation soil layer.The water-proof system was made of two cloth and one membrane water-proof layers planted under the clay layer on the backfill soil platform，and two cloth and one membrane water-proof layers in the contact area between the gravel layer and the anti-slide pile.The field treatment results show that this method can effectively prevent the slope from instability and failure again.