In SaaS Applications, the data of tenants are stored in the untrusted service provider side, this case increases the risk of data leakage, and becomes the brief reason to prevent people and enterprise from taking SaaS mode for their applications. Correspondingly, confidentiality-guarantee has become the key factor of its large scale promotion. In this paper we propose a general secure mechanism that allows the sensitive data of tenants to be stored in encrypted mode, which guarantees data confidentiality on the assumption that application server is trusted, and then put forward the analysis of its security and performance.