Abstract: In the process of ballistic missile penetration, modern active jamming systems can generate decoys resembling true target echoes in aspects of energy, waveform, or even phase modulation. These decoys can share the radar signal processors coherent processing gain, making conventional signal-based discrimination methods invalidate and even form multiple false tracks at the data processor. In this paper, motion models of active decoys in typical coordinate systems (CS) are derived theoretically, and the motional characteristics of active decoys are analyzed in detail. These motion models can reveal the intrinsical dynamics differences between physical targets and active decoys. Firstly, uniform mathematical model is built up to derive the motion models in East-North-Up (ENU) CS, Radar spherical CS and Earth-centered fixed (ECF) CS. Secondly, the orbit, velocity and acceleration characteristics of active decoys are analyzed on the basis of motin models. And thirdly, performance analysis due to related elements are also covered. This study makes a contribution in that it has provided motion-based discrimination algorithms with theoretical basis.