The invention discloses an air compressing device of an air compressor. The air compressing device is used for improving the reliability of air compression of the air compressor. The air compressing device comprises a base, a bearing end cover, a spindle, a movable disc installation cover, a movable disc and a fixed disc. The bearing end cover is fixedly connected with the base. A spindle installation through hole is formed in the middle of the bearing end cover. A spindle bearing matched with the spindle is fixed in the spindle installation through hole. The bearing end cover is used for covering the movable disc and the movable disc installation cover, and outside dust or particles are prevented from entering the movable disc or the movable disc installation cover. The spindle penetrates through a spindle bearing to be connected with the movable disc, so that the spindle is supported by the spindle bearing during movement, shaking of the spindle during movement is effectively limited, the movable disc can make eccentric motion stably along a preset rail along with the rotation of the spindle, and thus the reliability of the vortex type air compressor is effectively improved.