The spindle unit with independent sleeve structure is equipped with high-precision special bearings for the spindle, and the lubricating grease for German bearings is used, which greatly reduces the thermal deformation of the spindle unit and improves the thermal stability and accuracy. The maximum speed can reach 4500rpm (A2-5 head) or 4000rpm (A2-6 head); The high rigidity, high speed and high precision of the spindle unit enable the whole machine to be competent for various rough and finish machining.