The factors influencing IR decoy burning continuous time are determined by analyzing the circumstance and operating process of IR decoy. On the basis of treating the parameters of guidance system and carrier relative data, and rationally removing the relative circumstance factors, through the movement model of IR decoy, the distance between airplane and IR Decoy is derived from two ways when the IR decoy executes an effective jamming, finally an simultaneous equation is established to analyze the calculation method of continuous time required to IR Decoy.