The invention relates to a device for picking an outside diameter dimension of a bearing, and belongs to the mechanical manufacturing field. The device consists of a classification support, a classification ribbed plate, edge baffles, a conveyer belt, air cylinders, ultrasonic distance sensors, sensor mounting plates, bearing clamping plates, detection head emitters, rollers, detection head receivers, a main fixing frame, vertical mounting plates, a motor, a coupler, a belt and belt pulleys, wherein the classification support is welded on the rear end of the fixing frame; the vertical mounting plates are welded on the middle part of the main fixing frame; the rollers are installed on the both ends of the main fixing frame, the conveyer belt is arranged outside the rollers, one side of one roller is connected with one belt pulley, and the belt is arranged outside the belt pulleys; the motor is connected with the coupler, which is connected with the other belt pulley. The device has the advantages of being simple in design and easy to operate, combining the mechanical structure and modernized control, realizing automatic production, improving production efficiency and saving time and effort.