The invention is a fan, comprising a fan frame, where a central pole is formed in the fan frame; a bearing combination held in the central pole and comprising an oily bearing and a roller bearing; a rotor arranged in the fan frame and comprising a main body and a rotating shaft extending out from the top of the main body into the bearing combination; an isolator fixed on the central pole and arranged between the oily bearing and roller bearing to prevent impurities in lubricant of the oily bearing from flowing into the roller bearing with the lubricant.