As a world-renowned heritage site, the Ming Great Wall in Qinghai Province, is an example of an earthen site that is seriously threatened by a series of deterioration. Its damage assessment is the precondition for further protection planning and implementation, but related research was found to be scant. To fill this gap, we explore to study its damage assessment by applying Fuzzy-AHP and AHP-TOPSIS to determine the damage assessment levels for 18 earthen sites selected from Qinghai Province, combined with their occurrence environment, engineering properties of rammed earth, deterioration characteristics, and building technologies. After obtaining and comparing results, the AHP-TOPSIS is indicated to be much closer to the real damage conditions. Therefore, this method is proved to be more suitable for the damage assessment of earthen sites in Qinghai Province. This study also holds the potential application of the AHP-TOPSIS in the damage assessment for other earthen sites in Northwest China.