A rotary driving mechanism includes a support stand, an air feeding assembly, and a driver. The air feeding assembly includes a bearing base, a rotating member, two first ventilating joints, and two second ventilating joints. The bearing base is coupled to the support stand and defines an inner circular surface. The rotating member is rotatably received in the bearing base and resists the inner circular surface. The rotating member defines two circular grooves at an outer periphery thereof and two channels therein. Each circular groove is in fluid communication with one of the channels. The first ventilating joints are coupled to the bearing base and respectively in fluid communication with the circular grooves. The second ventilating joints are coupled to the rotating member and respectively in communication with the channels. The driver is coupled to the rotating member and in communication with the second ventilating joints.