The invention provides a robotic arm for transporting a substrate in an ultrahigh vacuum including a carrier module and a drive module. The drive module includes a magnetic coupling, a first transmission module, a second transmission module, and a third transmission module. The magnetic coupling includes an inner shaft and an outer shaft. The first transmission module drives the first active unit of the magnetic coupling to turn a first passive unit of the inner shaft by magnetic force. The second transmission module drives the second active unit of the magnetic coupling to turn a second passive unit of the outer shaft by magnetic force. The third transmission module drives the magnetic coupling and the carrier module to perform vertical movement. The carrier module will achieve rotational motion or extending motion when the inner shaft and the outer shaft are driven by the first transmission module and the second transmission module of the drive module.