Spindle loose force is insufficient or unsuccessful in the machining process of CNC machining center.To solve this problem,the action relationship of the loose broach mechanism was identified by the TRIZ system component analysis,the root reason of affecting loose tool was found by causal chain analysis of spindle loose broach system.Finally,the optimized design scheme was proposed by using the material field model analysis method of TRIZ theory and the principle of AD independence.The spindle loose force and screw strength of the new scheme were calculated and analyzed under actual working conditions,and the loose tool rod model was built and simulated.The results show that the maximum displacement is 6.995 μm and the maximum stress is 45.24 MPa,which can meet the requirements of structural design.Finally,through the physical field test,when the hydraulic pressure is 5 MPa,the loose tool stroke,loose tool force,and cutter loose quantity are in line with the production requirements.The rationality of the optimized design scheme is verified.