Seat belt retractor

A seat belt retractor, wherein the seat belt retractor comprises a pretensioning component and a winding component connected to the pretensioning component, wherein the winding component is used for winding the seat belt, wherein the pretensioning component includes a stop wheel and a ball gear, wherein the ball gear is sleeved on the stop wheel in an anti-torsion manner, wherein the stop wheel is provided with a plurality of first curved surfaces arranged in the circumferential direction of the stop wheel, wherein the ball gear is provided with a plurality of second curved surfaces arranged in the circumferential direction of the ball gear, wherein the first curved surfaces and the second curved surfaces are equal in number and correspond one-to-one, wherein each first curved surface and its corresponding second curved surface together enclose a ball chamber for accommodating a pretensioning ball, wherein the centers of a plurality of ball chambers are located on a preset plane together, wherein a portion of the second curved surface together with the first curved surface is located on one side of the preset plane, wherein the other portion of the second curved surface is located on the other side of the preset plane.