A water tank mounting structure and a ventilation treatment apparatus for such structure. The water tank mounting structure comprises a cavity for containing a water tank and a side wall defining the cavity, wherein the side wall comprises an inner side wall spaced apart from an outer side, a first gas hole provided in the inner side wall, and a second gas hole provided in the outer side wall, both holes arranged in a staggered manner perpendicular to the side wall. The arrangement of the double-layer side wall, and the first and second gas holes in the inner and outer side walls, respectively, allows for hot gas in the cavity to be effectively removed. The staggered arrangement of the gas holes allows for water to flow downward along the side wall without invading the cavity when water enters through the second gas hole. A waterproof effect is achieved.