For the issue of the discretionary access control (DAC) model safety analysis,a logic method is proposed.This method takes the GD model as the classic DAC model and Prolog as the basic language to describe system states and state transfer rules.A general program based on this logic method is proposed for DAC safety analysis,but this program may never be terminal for some safety analysis goal.The safety analysis algorithm is achieved by simplifying the general program according to the property of the DAC model state transfer rules.This safety analysis algorithm is easier to understand and implement than the previous algorithms and its time complexity is O(N+M+T),in which N,M,and T are the numbers of the rights with copy flag,the policies for right transferring,and the policies for right permitting,respectively.