Abstract: The spindle is the "heart" of machine tool. The performance of the spindle directly determines usage situation and behavior of machine tool, as a main functional component. The first "defender" of the spindle is the front-end seal structure. Large-flow cooling and machining dust can easily contaminate the spindle and bearings. Therefore, the design and selection of the front-end seal structure of the spindle should be seriously considered during the design of the spindle components. This paper focuses on how to select proper type of the spindle and its front-end seal structure, according to the structure and processing conditions of the machine tool.