The invention discloses a reverse torsion preventing tool for a screw drill. The reverse torsion preventing tool comprises a track supporting device, a connecting device, a locking device and the like. The track supporting device provides a sliding track for the reverse torsion preventing tool; the connecting device and the locking device constitute a main body of the reverse torsion preventing tool; and the locking device is engaged with a plug drilling single pipe through tong teeth, and thus a pipe column during plug drilling of the screw drill is formed. The reverse torsion preventing toolfor the screw drill is easy to operate, safe and reliable, mounting and debugging can be completed by two construction personnel during operation, automatic locking and unlocking can be achieved during drilling, and manual operating is not needed; and the safety risk during operation is effectively reduced, the plug drilling efficiency is improved, and the problem of reverse torsion generated during plug drilling of the screw drill is eliminated.