Motorized spindle is high speed machining unit combined with hidden motor and machine tools axis, which has advantages of high speed, stepless transmission, zero transmission chain, and is applied in machine center widely. Key technologies are combined together in motorized spindle designing, such as high speed motor, bearing, manufacturing and assemblage. It is strict in assembling to guarantee rotating precision and dynamic balance and is different from common machine tools designing due to characters of high speed and hidden motor. Hydrostatic bearings have advantages of high carrying capacity, lower friction, and better holding precision, the heat problem is extrusive, but the future of hydrostatic motorized spindle is considerable. Modal and thermal performance analyses are necessary for motorized spindle designing. With modal analysis, inherent frequencies are confirmed, which could be of help to avoid sympathetic vibration in machining. It provides evidence for designing cooling system of thermal performance analysis.