Numerical control system with cutter changing function and numerical control method of numerical control system

The invention discloses a numerical control system with a cutter changing function and a numerical control method of the numerical control system. The numerical control system comprises a numerical control device, a driving device and a processing device. A detecting machine of the processing device detects the position of a cutter spindle in a Z-axis direction and the rotating angle of the cutter spindle, and outputs the rotating angle and the position information of the cutter spindle to the numerical control device; the numerical control device calculates out the rotating speed of the cutter spindle according to the rotating angle of the cutter spindle, generates a judgment signal after judging the rotating speed, the position and the rotating angle of the cutter spindle, and plans the rotating speed, the position and the rotating angle of the cutter spindle according to the judgment signal so as to perform cutter changing; when the numerical control system performs the cutter changing, the decision whethe