The invention discloses a control system and method for a mechanical arm. The system comprises a feeding mechanism, a first electromagnetic valve, a second electromagnetic valve, a third electromagnetic valve, a fourth electromagnetic valve, a servo motor, a fifth electromagnetic valve and a controller. The controller is electrically connected to the feeding mechanism, the first electromagnetic valve, the second electromagnetic valve, the third electromagnetic valve, the fourth electromagnetic valve, the servo motor and the fifth electromagnetic valve. The control system and method for the mechanical arm have the advantages that through a starting program which is connected into a CNC lathe in series, the control system can be widely applied to a numerically-controlled machine tool and a machining center, so that seamless joint of the CNC lathe and the mechanical arm is achieved, and full-automatic unmanned machining is realized.