Abstract: The characteristics of cloud computing such as openness, sharing, make the access control more complicated in cloud computing than it in traditional environment. In order to guarantee the security and reliability of cloud users and the data on the cloud server in the accessing process, this paper put forward an access control model named CT-RBAC in cloud computing. This scheme divided the security level of the data on the cloud server and cloud users, and introduced the set of task situation, what's more, it achieved the access control policy from five aspects. Finally, it gave out the implementation process of cloud users access the data in the cloud. The analysis results indicate that CT-RBAC has its obvious advantages. This scheme improves the monitoring ability of the object owner to the cloud server, guarantees the security and reliability of data, and ensures the well flexibility.