A segmented cage for a ball bearing is provided, having multiple independent spacers, distributed at intervals between rolling elements of equal number to the spacers. A pocket slot is formed on each of two sides of each spacer in a position of contact with the rolling element, a concave curved surface adapted to hold the rolling element is formed in the pocket slot, and opposing pocket slots of adjacent spacers are matched to form a cage pocket for enveloping the rolling element. At least one main oil hole is formed in each spacer, running through the interior of the spacer and opening at the pocket slots on the two sides. The rolling element is held by the concave curved surface such that the rolling element is unable to contact with an opening edge, in the pocket slot, of the at least one pair of main oil holes.