The invention discloses a lock hole protecting device, and aims to provide the lock hole protecting device capable of effectively preventing the problem of incapability of normally opening a lock caused by such bugs as spiders and cockroaches climbing into a lock cylinder hole of the lock and capable of preventing the problem of influence on normal opening of the lock due to rusting of the lock cylinder hole of the lock caused by flooding. The lock hole protecting device comprises a shielding plate, a lock cylinder hole insertion plate arranged on the surface of the shielding cover plate, an accommodating tank formed in the surface of the lock cylinder hole insertion plate, an airbag bag arranged in the accommodating tank, an airbag bag inflation nozzle formed in the airbag bag, a transverse air guide hole, a longitudinal inflation hole and a longitudinal connecting hole formed in the lock cylinder hole insertion plate, an annular mounting groove formed in the surface of the shieldingcover plate, an annular inflation sealing ring arranged in the annular mounting groove, a transverse plunger hole formed in the shielding cover plate, a piston body slidingly arranged in the transverse plunger hole, and a first connecting hole formed in the shielding cover plate.