An additional numerical control milling machine automatic control system provided by the invention comprises a cabinet, a spindle box, a spindle, a mechanical arm, a mechanical paw, a numerical control system, a mechanical paw control system, a command parser, a command cache, a coding support library, and a coding system. The spindle box is arranged in the middle of the cabinet, and the spindle is arranged at the bottom of the spindle box. The system of the invention can be directly installed on numerical control milling machines of some models without the need to change the structure of existing numerical control milling machines. The installation difficulty is high for enterprises, the degree of reception is high, and the market prospect is good. The human cost and material cost for tool replacement are reduced greatly, so that the cost is reduced greatly for enterprises. The system is easy to adjust and highly adaptable, can be used to better complete tool replacement and work piece replacement or adjustment, can greatly facilitate full automation, is convenient to use, and can effectively reduce the burden on operating personnel.