The invention discloses a backfilling device for returning corn straws into a field, and belongs to the field of agricultural machinery. The backfilling device comprises a bracket, a material pickingdevice, a crusher, and a backfilling device, wherein the material picking device comprises a material charge passage, a fan, a material picking motor and a blocking plate; the lower end of the material charge passage is provided with an opening, and the material picking motor is used for driving the fan to rotate; the crusher is provided with a material falling pipe, and the lower end of the material falling pipe is provided with an opening; the backfilling device comprises a drive shaft, first drive gears, second drive gears, a drive wheel, driven wheels, an excavation belt, a first support arm, a second support arm, a hydraulic cylinder and an excavation roll, the drive shaft is in drive connection with a power device, the first drive gears are connected with both ends of the drive shaft, each second drive gear is connected with the corresponding first drive gear, the drive wheel and the driven wheels are coaxially arranged on the second drive gears, the excavation belt is matched with the drive wheel and the driven wheels, the second support arm is connected with the first support arm, the hydraulic cylinder is arranged on a bracket, and the excavation roll is in drive connection between the driven wheels. The backfilling device has the advantages that the deeper soil is excavated by the excavation roll to form a gap, the crushed straws fall into the gap, and the influence to the planting effect due to the overhead treatment of the shallower soil by the straws is avoided.