Abstract: The problems of damage to the spindle claw petals and the tool magazine tool claws caused by the deviation of the tool change position and the deviation of the fit between the spindle and the tool shank during the tool change on the machine for the servo tool magazine are focused on. Research on the in-machine tool change detection and fool-proof mechanism is conducted. The motor load data of the tool magazine and the motion axes on the CNC machine tool are monitored in real time to judge the deviation of the tool change position and the state of the spindle releasing and clamping the tool. An effective in-machine tool change detection and diagnosis mechanism is formed through comprehensive analysis of the deviation data, and by applying the trend analysis method and the fuzzy algorithm.