The invention discloses an excavation construction method of an assembled reinforced scarifier for a plateau permafrost region. The method is characterized in that the assembled reinforced scarifier is assembled on a crawler excavator and can be exchanged with a bucket to be assembled and used; a hydraulic piston of the crawler excavator is utilized to push a tooth seat of the scarifier to change the excavation direction and a working point of a bucket hook of the scarifier, wherein the scarifier comprises a main board, a hanging lug plate, a rear plate, a bucket lug plate, a bucket lug sleeve, bucket teeth, the tooth seat, a protecting plate and other spare parts. Compared with a common excavator which is difficult to damage the structure of the permafrost layer during excavating and can remove the permafrost by layers only after the permafrost in the top layer is molten, each layer of the permafrost is limited to be damaged between 20 and 30cm, and collapse easily occurs due to the unstable melting of the permafrost on a side slope after the damaging work is performed for a longer term, the assembled reinforced scarifier is out of the limitation on the frosting degree and thickness and the like of the permafrost layer, and each layer of the permafrost can be damaged about 50cm in thickness, so that the work of breaking the permafrost layer can be finished within a short time, and as a result, the construction progress can be increased, and the construction period can be saved.