Active defense is a novel combat technology that significantly enhances the effectiveness of aircraft air combat. It is a process in which the aircraft intercept enemy missiles by actively launching missiles to avoid their threats. The traditional attack zone models fall short in addressing the computational needs for decision-making support in active defense air combat. In order to solve this problem, this paper establishes a new model to evaluate the decision-making index of air combat, namely the dynamic attack zone under the condition of active defense of the enemy, and analyzes the connotation of the dynamic attack zone. Firstly, based on differential game theory, a game model of target-defensive missile-attack missile is established, and the optimal pursuit-escape control strategy under the background of dynamic game is solved. Then, according to the actual constraints of active defense process, a dynamic attack zone boundary solution strategy based on improved advance and retreat method is designed. Finally, a variety of typical situations are selected to simulate and verify the dynamic attack zone model. The experimental results show that the dynamic attack zone under the condition of the enemy’s active defense can accurately represent the launching range of the attack missile, which provides more clear quantitative guidance information for air combat decision-making.