Abstract: Based on the requirements of the spacecraft assembly, this paper proposes a flexible force control method on the robot arm: a 6-axis force/torque sensor is mounted between the tool and the end of the robot arm, the operator operates the load by hands directly, and the system can obtain the force/torque information caused by operator's hands through a gravity compensation algorithm, then the force/torque information is used as input parameters to control the robot arm movement with the hands. The detailed scheme and algorithms are presented in this paper, and preliminary experiments were carried out to test the method. The experiments show that with the new method, the installation of a heavy equipment in a small room for the spacecraft would take much less time.