As a new mode of service, cloud computing receives the favour of various enterprises in recent years. Though there are three kinds of deployment models to be chosen, enterprises also worry about the storage and transmission security of data. A method of Attribute Based Access Control(ABAC) was used to ensure that only authorized users had access to the data in the cloud. In addition, the method of rough set attribute reduction method was used to reduce the redundant attributes, retain authority conflicts and speed up the access time.