The invention relates to a self-aligning ball bearing integrated with a planet gear speed reducing device. The device comprises an input shaft, inner rings, a rolling body, a cage, outer rings, an outer ring sun gear, a planet gear, an input shaft sun gear, a planet carrier and screws. The inner rings and the outer rings of two bearings are respectively provided with small grooves; the small grooves fit to form a small cavity; the rolling body and the cage are mounted in the small cavity; the axial widths of the outer rings of the two bearings are wider than the axial widths of the inner rings; the outer rings of the two bearings are arranged in a form of stairs, and are connected through the screws to form a cavity; a gear is mounted on the inner wall of the cavity of the inner ring of one bearing, and is called as the outer ring sun gear; the input shaft is in interference fit with one gear inner ring; a gear is mounted at one end of the input shaft extending into the cavity, and is called as the input shaft sun gear; the planet gear is mounted between the two sun gears, and is supported by the planet carrier; and the planet carrier is in interference fit with the other bearing inner ring, and is also called as an output shaft.