The invention provides an adjusting device of an auto seat headrest, which belongs to the technical field of automobile components, and solves the technical problems, such as that an adjusting device of an existing auto seat headrest is inconvenient to operate, complicated in adjustment and high in cost, and the like. In the adjusting device of the auto seat headrest, the auto seat headrest comprises a bed plate, a backrest and a headrest. The adjusting device provided by the invention is characterized by comprising a lead screw, a nut and a motor, wherein the nut is fixed on the backrest, the lead screw passes through the nut, one end of the lead screw is connected with the headrest by a connecting structure, and the other end of the lead screw is connected with an output shaft of the motor by a transmission structure. The adjusting device provided by the invention has the advantages of reasonable design, convenient operation, good lifting effect, low cost and the like.