Abstract:Traffic Alert and Collision Avoidance System(TCAS) plays an important role in the Aircraft Environment Surveillance System. It can help to reduce the risk of midair collisions between aircrafts. It is crucial to flight safety enhancement. TCAS is the air collision avoidance system without ground instrumentation. It detects the plane by air traffic control responder beacon system, and makes warnings for potential collision targets. Targets Tracker is important to the TCAS. It not only provides the states of targets, but predicts the states of targets in the future. Aimed at the target motion uncertainty and dynamic model nonlinear, Interacting Multiple Model algorithm based on Extended Kalman Filter(IMM-EKF) is proposed. Simulation results indicate that the proposed algorithm provides precise tracking of target, which works well for traffic alert and collision avoidance.