The present disclosure provides a robot arm, including a pedestal, a support arm on the pedestal and configured to support a substrate, a driving system configured to drive the support arm to move, and a substrate alignment device connected to the support arm. The substrate alignment device includes a first position information collection unit configured to acquire first position information of the substrate when the substrate is on the support arm at a first position; a deviation information acquisition unit configured to acquire position deviation information of the substrate in accordance with the first position information and second position information of the substrate in the case that the substrate is located at a standard position, and an adjustment unit configured to generate control information in accordance with the position deviation information, thereby driving the support arm by the driving system to place the substrate at a target position.