The positive factors of the cloud computing: the great commercial value, the cheap and convenient use, has been recognized widely. But there are many risks on security. These security risks will greatly restrict the development of cloud computing. Cloud security risks such as: the cloud platform is easily vulnerable, cloud resources is easily abused, the cloud platform data is accessed by unauthorized user or the data is missing, the violations in the network is difficult to trace and survey, and the service providers replacement will affect the migration of the users data and services. So we research the virtualization technology, data backup and disaster recovery technology, encryption technology of data storage and transmission, the authentication technology of service providers and users, risk assessment, and legal constraints and safety training. Our research is strived to obtain a secure cloud computing environment.