Evasive maneuvers and decoy deployment are effective measures against infrared (IR) air-to-air missiles for fighters. In this study, both aspects were considered: barrel roll maneuver and unpowered point source decoys. For practical purposes, the interference process, movement characteristics, and influence mechanism of the decoy on the missile guidance system are expounded, in which the conditions needed for the barrel roll maneuver and the force of the decoy are considered. In addition, the air-to-air missile is assumed to adopt the true proportional navigation law or augmented proportional navigation law, and the decoys are launched in the conventional mode or emergency mode. Linearized time-varying models and adjoint models for barrel roll maneuvers with decoy deployment influence on missile guidance precision are established. The correctness of these models was verified by a simulation result analysis and comparison. The miss distance is an important parameter for characterizing the performance of an air-defense missile. The average miss distance and percentage of maximum miss distance were proposed to analyze the adjoint model results. Based on the work mentioned above, the barrel roll rate and the transition step maneuver angle of the target aircraft, as well as the simultaneous launch quantity, the period between successive launches, and launch direction policy on the miss distance are analyzed to provide strategic references for fighters against IR air-to-air missiles.