To study the intelligent reasoning of the process to grind machine tool spindle, a grinding process software is developed to satisfy its intelligent manufacturing. The software includes several modules, such as the basic database of the intelligent grinding process for machine tool spindle, the process database, the optimized examples of process & intelligent reasoning, and the automatic numerical control & programming. Experiment on the CNC outer grinding machine shows that the software could significantly improve the accuracy of the decision making of the spindle numerical control grinding process up to 96%, and that the decision time is reduced by 50%, thus improving the processing efficiency.