Data security is one of the leading concerns and primary challenges for cloud computing. This issue is getting more and more serious with the cloud computing became popular .Once users data is uploaded, it must be drifted away from the user's control, and it is no longer security. In this paper, the nine key data security principles were analyzed in depth on the basis of a comprehensive summary of the data need to be protected. Finally, six key technologies of data security were proposed. All of these can guarantee the data security throughout the whole lifetime.