This paper aims at deepening our understanding of the dynamics performance of the drag-free satellite at ultra-low frequency. A coupled modeling of dynamics which incorporate orbit dynamics, environment disturbance and interaction between the satellite and the proof mass is presented. Frequency bandwidth under investigation is extended from the micro-vibration frequency bandwidth (10 mHz to 100 mHz) to a broader bandwidth (0.1 mHz to 100 mHz) which partly covers the micro-gravity frequency bandwidth (<10 mHz). As two stringent requirements of drag-free satellite, the distance between the satellite COM (center of mass) and the proof mass COM, as well as the residual non-gravitational acceleration of the proof mass, is studied under the impacts of the atmospheric drag, the interaction between the satellite and the proof mass, and the orbit motion.