Repair and troubleshooting of the electric spindle of Mori Seiki machine tool: replace the front bearing and lubricating grease, adjust the bearing clearance, manually grind the positioning surface of the taper hole in the spindle, check with coloring method, reinstall the repaired spindle into the spindle box, check the radial runout with a dial gauge, conduct trial machining, the spindle temperature rise and noise are normal, the machining accuracy meets the machining process requirements, and the fault is eliminated.