Deep hole machining accounts for a large proportion in machining. Due to the special depth of the hole being processed, the conventional deep hole drilling fixed cycle can lead to overheating of the tool after several times of drilling. Using the macro functions of the FANUC system, a new G code is developed to gradually reduce the depth of the drilling hole when processing deep holes. After being verified by the GLU28x40 CNC, the newly defined G code is input and programmed according to the prescribed syntax, Equivalent to a fixed loop implanted in the control system. When machining deep holes, it can effectively alleviate the problem of excessive tool temperature during the pecking drilling process and improve processing accuracy.