In order to estimate the states of the machine tool spindle system during the course of its operation, this paper proposes a deterioration method based on the complexity of the nonlinear system by monitoring the relative index. The vibration signals generated by the workpiece spindle when the grinder machine tool operation is idling were used as the objects of analysis, and the complexity relevant index is used to judge the states of the workpiece spindle of the grinding machine during several months of operation. The analysis results showed that the complexity of the vibration signals generated by the workpiece spindle system increased as the time in use increased. In order to verify the validity of the deterioration analysis, the complexity index is used to analyze the dates of the deterioration bearing published by CWRU. The results showed that the complexity is an effective method for deterioration analysis.