Abstract: A gravity unloading method based on robot force/position control is proposed for the gravity unloading requirements in ground testing of space deployable mechanisms. The robot applies the lifting force to balancing the gravity effect of the deployable component, and the lifting point on the robot follows the deployment motion trajectory through force/position control, achieving gravity unloading throughout the deployment process. For the deployment testing conditions of a specific antenna, the calculation methods of the adjustment in the position control and force control of the robot are given respectively. A calculation method for the lifting force is provided for the case that the lifting point does not coincide with the center-of-gravity of the deployable component. In addition, an online identification method for the mass characteristic parameters of the deployable component is provided for the case that the mass characteristics of the deployable component are not accurately known. A recognition method based on tangential force judgment is proposed to get the starting and stopping timing of robot following unloading movement. In the experiment, a servo motor with a rated output torque of 2.39 N·m is used to drive a simulated component with a gravity torque of 153 N·m. A 6-DOF (degree of freedom) industrial robot is used to follow the component for gravity unloading, achieving a maximum lifting force prediction error of 1.3 N after the deployment angle reaches 10°. The gravity unloading for the entire deployment process is achieved, ensuring that the joint torque remains within the rated torque range of the motor in the entire deployment process.