Abstract: To determine the safe headway of adaptive cruise control vehicles, the platoon stability based headway was proposed by using the interconnected systems stability theory. Based on the following control model of vehicles, the local stability of platoon was analyzed, relationships between the safe headway and the global stability of platoon were studied, and the determination method of this headway was given. The test results show that the safe headway determined by the proposed method can ensure the securities of all vehicles in the platoon in different situations.