The invention relates to the field of manufacturing of deep groove ball bearings and angular contact ball bearings and provides an aligning device for a ball-filling gap of grinding bearing. The aligning device comprises a fixed seat, a column, a connecting block, a slide bar, a slide block, a rotating shaft, a measuring arm and a gap aligning sheet, wherein the column is fixed on the fixed seat, the connecting block is connected to the column and the slide bar, the slide block is arranged on the slide bar, the rotating shaft is further mounted on the slide block, the slide bar on the slide block is parallel to the rotating shaft in axis, the slide block can freely slide and rotate on the slide bar, the rotating shaft is fixedly connected to the measuring arm, and one end of the measuring arm is fixedly connected to the gap aligning sheet. According to the aligning device and the aligning method provided by the invention, locating grinding on a gap can be performed precisely and continuously, so that the grinding machining precision of the ball filling gap of the bearing is improved, the shape precision and the surface roughness of the gap are guarantee, the grinding gap defect is avoided, and meanwhile, the aligning device is simple in structure, convenient to use and low in cost, and the work efficiency can be greatly improved.