A gun attachment holder includes a device holder, which has a coupling groove detachably coupled to a coupling flange of a gun and a sliding groove transversely extending across the coupling groove, two locking members reversely arranged in parallel and slidably mounted in the sliding groove and movable between a locking position to lock the device holder to the coupling flange of the gun and an unlocking position to unlock the device holder from the coupling flange of the gun, and a torsional spring set in between the locking members to hold the locking members in the unlocking position.