Abstract: In order to reduce the influence of loose broach force on the spindle system of CNC machine tool and improve the service life of the spindle, the original the loose broach system of the spindle of NC boring milling machine was analyzed and optimized. Firstly, the paper analyzed and designed the spindle loose broach mechanism of the CNC boring milling machine, and established a 3d model. Secondly, the force of the spindle in the two states of loose cutter and broach were studied, and the loose cutter force which has a great influence on the life of the spindle bearing was obtained. Finally, TRIZ theory was used to optimize the spindle loose broach system. The results indicate that the optimization does reduce the influence of the loose broach force on the spindle system without reducing the loose broach force.