Provided is an improved method for preventing electrical elements of a slab demagnetizing device from being affected with damp or leaking electricity. The upper end of a machine frame (4) is connected with a supporting plate (7), a work panel (3) is arranged on the supporting plate, the electrical elements (5) of different kinds are respectively arranged around the machine frame or inside the machine frame, and a water dripping outer edge (1) is connected to the edges around the horizontal supporting plate. The water dripping outer edge is folded towards the interior of the machine frame for forming a damp-proof folded edge (2) tilting upwards, cooling liquid (6) accumulating on the work panel only can flow downwards along the water dripping outer edge, the cooling liquid can not flow down along the damp-proof folded edge tilting upwards, and therefore the electrical elements (5) can not be affected with the damp or leak the electricity under the condition without being soaked by flowing of the cooling liquid, the safety reliability of the electrical elements is greatly improved, production of the slab demagnetizing device can be carried out normally, and the safety of operation personnel is guaranteed. Damage to the electrical elements due to affection with the damp or electricity leakage can be avoided, and the maintenance cost is reduced.