This paper presents a new approach of the Interacting Multiple Model (IMM) algorithm by introducing a non-linear guidance model from the guidance law.Unscented Kalman Filter (UKF) is applied to deal with the non-linear models in the IMM algorithm.Factor of Trajectory Convergence (FTC) is introduced based on the basic characteristic of the missile trajectory to adjust the transition probability online.The simulation results demonstrate that the guidance model based FTC adaptive IMM-UKF algorithm works perfectly in the tracking system.