Abstract: Aiming at the requirement of ultra low-level microgravity environment for scientific experimental loads, a scheme of microgravity accompanying flight experimental module for China Space Station (CSS) based on gravity gradient passive stabilization was proposed. The accompanying flight experimental module flies independently of CSS to avoid the complex and variable interference sources from CSS. The ultra low-level microgravity of the experimental module during accompanying flight was achieved by an attitude and orbit control method with vibration free and micro-acceleration, i.e., the attitude control was implemented by means of gravity gradient passive stabilization combined with active magnetic control. The orbit height and attitude control scheme was realized by adjusting the yaw-angle to change the windward area, so as to ensure the safety of companying flight. Meanwhile, the experimental module fully utilized the in-orbit resources of CSS by configuring the guidance actuator, as well as installing the pose sensor and robotic arm target adapter. The simulation analysis shows that the experimental module can provide a long-term and sustained ultra-low level microgravity environment of 4.9×10^-7g₀ for the payload.