A novel time-sharing driving system for robots was proposed. By using the time-sharing driving system, one actuator can drive 2 independent outputs. The working principle of the driving system was introduced and a flexible robot arm was designed based on the driving system. The flexible arm has 6 DOF and only 4 actuators. With small number of actuators, the control and sensing system of the robot arm can be simplified at a large scale. The control and mathematical model of the robot arm are analyzed, which can provide more theoretical principle for design and optimization. The proposed robot arm and the time-sharing driving system are rather flexible, highly compliant and safe for human interaction. They can be widely used in many kinds of automatic system that needs manipulators and simple control and sensing system.