Abstract: The security topic in application and development of cloud computing is one of the greatest concerns．Aiming at the requirement of security level quantification in cloud computing service,based on classified protection in our country and learned from the cloud computing risk control and security assessment frameworks designed by European and American institutions,a cloud computing security assessment indexes system was built up through Delphi method,and the weight of each index was calculated with analytic hierarchy process．According to this indexes system,fuzzy comprehensive analysis method was introduced to the evaluation of a cloud computing instance．The case study shows that this model can effectively quantify and assess the security level of cloud platform.

Key words: Cloud computing,Security assessment,Classified protection,Analytic hierarchy process,Fuzzy comprehensive evaluation