Machine tool spindle is the object to be optimized and designed. Combined the optimum design idea and Matlab, the model optimization to machine tool spindle was put into practice with penalty function. Then modal analysis was carried out by ANSYS. The first six lowest orders of the spindle, mode of vibration and critical speed of revolution were analyzed. And the rationality of structure optimum design of the spindle was verified. This research provides references to the structure optimum design of machine tool spindle.