The invention discloses an automatic overturning soil discharger applied to the field of underground tunnel engineering equipment. The automatic overturning soil discharger comprises a muck hopper and a lifter, wherein the left side face and the right side face of the muck hopper are respectively provided with a main lifting lug; the lifter is hinged with the main lifting lugs; and a connecting line between the two main lifting lugs is lower than the first barycenter of the muck hopper when the muck hopper is filled with the muck, and is higher than the second barycenter when the muck hopper is under the unloaded state, and the connecting line between the two main lifting lugs is not intersected with the gravity action line of the first barycenter. According to the automatic overturning soil discharger, the muck hopper can be automatically overturned at 180 degrees so that the soil can be discharged, and the muck hopper can be automatically reset after being overturned. Thus the automatic overturning soil discharger is high in soil discharge efficiency, the soil discharging place and the height of the muck hopper when the soil is discharged can be conveniently adjusted, and the muck can not be splashed to the periphery when the soil is discharged.