In this paper, a new dynamic access control method with binary locks is proposed. Mainly, each file (or resource) in our system is assigned as many binary lock values as necessary. The access privilege of a user to a file is revealed by applying operations on the file's locks. Our method can be used to update the access right with little effort. Moreover, insertion or deletion of a user or file is simple due to operations on binary locks that are easy and efficient. Compared to other methods proposed so far, the computations of our method are simple and efficient, and the storage space required for our system is rather economical as well.