When prominence of security problems increasing,it is of importance to savethe sensitive electronic documents into database. The user-role mechanism is employed in the process of managing documents. However, it can't provide the flexibility of authorized access because of the dynamic generating particularity of the electronic documents which need maintaining continually. A tree model of entity authorization is introduced based on discretionary access control mechanism. The approach can grealty simplify the authorization, increase the flexibility and is more accordant with the practical requirement of enterprises.