Through long-term improvement practice and innovative design, we find that, during the design of the main shaft of machine tool, adopting good main shaft sealing structure can not only improve the sealing ability of the main shaft, prevent the external liquid and other impurities from getting into the main shaft, but also prolong the service life of the main shaft. Practice has proved that a good main shaft seal structure provides a necessary precondition for keeping the main shaft's good lubrication environment for a long time. In the design of the main shaft of the optical cold processing machine tool, it not only requires more and more strict manufacturing precision of the main shaft but also requires the good sealing performance of the main shaft, especially optical machine tools of fine grinding, milling, and polishing, because in the bad environment, the main shaft is often soaked in the fine grinding fluid or polishing liquid, and there is a certain amount of corrosion agent, abrasive and other substances in the fine grinding fluid. Once the material of the polishing liquid enters the bearings inside the main shaft of the machine tool, the precision of the main shaft of the machine tool will lose and the machine tool is damaged, at this time, what we can only do is replacing the whole main shaft part of the machine tool. Therefore, in the design of the optical machine tool, the most important problem is the sealing design of the main shaft, the main shaft design of common optical machine tools is not very good, their service life ranges from only half a year to one and a half years. This problem has been puzzling the domestic optical manufacturers. The durability of the sealing materials of the foreign machine tools is high, so their service life is a little longer than the Chinese machine tools and can reach two and a half years to three years. With years of design experience, we find that the optimized seal structure of the main shaft can greatly improve the service life of the main shaft. Under the same applicable conditions, if adopting the waterproof structure of the main shaft of our company, when the main shaft bearing accuracy (due to wear) exceeds the allowable tolerance, the components in the seal structure still have good sealing performance. When the main shaft is disassembled, there are no foreign objects inside the bearing. In general, a good main shaft seal structure can guarantee service life more than six years, and more than eight years under good maintenance.