This invention relates to an oil retaining structure of a spindle, wherein the outer peripheral surface of the spindle is provided with a first oil groove extending spirally along a clockwise direction and a second oil groove extending spirally along a counterclockwise direction. The first oil groove and the second oil groove across each other so as to form a plurality of collecting points. In operation, the oil film formed on the outer peripheral surface of the spindle will collect in the two oil grooves slowly, and the lubricating oil in the two oil grooves will bump into each other at the collecting points and then diffuse. As a result, an interior cycle is formed, which not only prevents the leaking of the lubricating oil but also makes the lubricating oil distribute evenly on the surface of the spindle.