Evaluation of the deterioration of earthen sites is fundamental for the scientific protection, management and use of earthen sites; however no evaluation system has been established so far. Based on the analysis of specific earthen sites and using theories and methods of geological engineering and geotechnical engineering, the deterioration of the earthen site foundation and the earthen site itself were evaluated by sequential analysis. Deterioration of earthen sites can be evaluated based on measurements of geological destruction, stability and surface weathering. The relatively mature engineering approaches and theories for evaluating geological destruction and stability can be adopted. For surface weathering evaluation, the weathering erosion rate, the condition of the earthen site and the value of the site should be considered; the degree of weathering and the heritage site''s value should be introduced into the model as a weighting coefficient. Using “fuzzy” mathematical theory, a new method was developed for systematically evaluating surface weathering.