Abstract: This paper describes a lattice－based access control model.All possible access control privileges pertaining to an object can be represented as the nodes on the access control lattice of the object.The update of access control changes the mapping of the subject access privilege from one node to another node in the access control lattice of object.Authorization right method and simple concurrency control algorithms for access control policy real－time update are given in the model.The model and algorithms are useful for concurrency environment in which multiple subjects access and modify data and access control policies,while the policies are in effect．