The utility model discloses a moisture -proof construction, use this moisture -proof construction the water tank, and use the air of this water tank can the water heater, wherein, moisture -proof construction includes: a housing, first gas pocket has been seted up to the casing, the inner bag, the inner bag is located in the casing, the heat preservation, the heat preservation is located the casing with between the inner bag, the heat preservation seted up with the dampproofing passageway of first gas pocket intercommunication, be equipped with the desicator in the dampproofing passageway. Thetechnical scheme of the utility model can reduce the moisture of invading among the inside humid air of casing, avoid electrochemical reaction's between inner bag and the heat exchanger emergence, improve the life of water tank and air ability water heater.