The cloud computing technology provides a more effective and safe platform for digital archives management. Focusing on the security of some factors of digital archives in the cloud computing condition is a significant project in the construction and operation of the Cloud Digital Archives. Through the analysis and the integration of various risks in cloud computing condition, which Digital Archives might face, the paper establishes the security evaluation index system including seven security factors,which are information system security, cloud computing technology security, digital archives security, laws and institutions security, support from internal organization, management and control security, objective and feedback. Using the Fuzzy Comprehensive Evaluation to estimate the mathematical model of the above-mentioned Cloud Digital Archives security evaluation system, the paper puts up with a set of security evaluation system which suits the Cloud Digital Archives.