The invention discloses a keyhole protective device, which comprises a shell, a keyhole cover and a locking mechanism, wherein, the keyhole cover is arranged on the shell; the locking mechanism comprises an autolocking armature, an armature hole, a key covering hole and a cover opening key which is matched with the key covering hole; the autolocking armature and the armature hole are respectively arranged on the shell and the keyhole cover; the key covering hole is arranged on the shell or the keyhole cover; the autolocking armature is matched with the armature hole; and the cover opening key comprises a cover opening key body and a key covering magnet which is arranged on the cover opening key body and matched with the autolocking armature. The keyhole protective device is matched with a key for use, which can effectively prevent a keyhole from being blocked and reinforce the theft-proof performance. Moreover, the keyhole protective device is simple in structure and flexible and convenient in use and operation and is a practical keyhole protective device.