Abstract: There are a great deal earthen heritage sites in the arid areas of northwest China. Based on the analyses of the deteriorations of the earthen sites in the arid area, the third grade classification system and definition about the deteriorations of earthen sites are established. The analyses are based on te the causes, the manifestation modalities, and the engendered mechanisms of the deterioratins. The deteriorations of the earthen sites were divided into the two major types: the nature breakage and the man breakage. The nature breakage had 5 secondary classifications, 14 tertiary classifications. it includes slice-peeling (the rain erosion-peeling, the wind erosion-peeling and the cranny-peeling), recess (the salt-recess, the wind-recess and the fluvial recess), cranny (the unloading cranny, the tectonic cranny, the deformation cranny and the building cranny),gulch (the cranny-gulch and runoff-gulch), life-form breakage (the animal breakage and the plant breakage). The man breakage has two types: the old breakage and the latter-day breakage.