The problem of guidance law identification of incoming missiles is discussed, and a method for identifying the guidance law of incoming missiles based on adaptive IMM-EKF is proposed. Assuming the utilization of the classical proportional navigation (PN) or augmented proportional navigation (APN) guidance law in the final attack stage of an incoming missile, a three-dimensional relative motion model is established between the missile and the aircraft. This model incorporates the missile's position, velocity, acceleration, and guidance coefficient as system state variables. To enhance system performance, an adaptive correction gain Kalman filter is specifically designed. Using the IMM approach, the guidance law of the attacking missile is promptly identified from a limited set of guidance filter models. By estimating the guidance coefficient, this method predicts the incoming missile's motion state and maneuver details. Simulation outcomes demonstrate that the proposed technique efficiently identifies the three-dimensional incoming missile's guidance law and precisely estimates its motion state.