The invention provides an automatic feather collecting device for a mechanical arm of a washing and dehydrating machine. The automatic feather collecting device comprises a machine head, a horizontal swing arm capable of moving up, down, left and right, an electric push rod and a feather collecting tube, wherein the electric push rod and the horizontal swing arm are fixedly mounted on the same horizontal plane, the front end of the electric push rod is connected with the machine head, and the back end of the electric push rod is connected with the horizontal swing arm, so that the front and back movement of the machine head can be controlled; the machine head is mounted at the front end of the horizontal swing arm, and comprises a spindle motor, a leather belt, feather scrabbling shafts, a bearing seat and feather scrabbling blades; the spindle motor is fixedly mounted in a bracket, and movably mounted on the horizontal swing arm through a rotating shaft and the electric push rod; the feather scrabbling shafts are fixedly mounted on the bearing seat fixed through the bracket, are connected with the spindle motor through the leather belt, and are driven to rotate through the spindle motor; the feather scrabbling blades are fixedly mounted on the feather scrabbling shafts, are driven to slowly get close to the inner wall of the dehydrating machine through the push of the electric push rod and the rotation of the feather scrabbling shafts, and spall the feather attached on the inner wall after dehydration layer by layer; the feather collecting tube is fixedly mounted on the machine head and the horizontal swing arm through the rotating shaft; the top end of the feather collecting tube is connected with a negative pressure air blower.