Igloo-shaped ammunition depots made of corrugated steel plate has a higher risk of condensation since the change in inside heat capacity is greater and its thermal conduction rate is higher compared to existing concrete ammunition igloos. Therefore, measures to prevent condensation are necessary. We suggested a method to create air gaps of 30cm in width in the back and on both sides of an igloo, as we thought that creating air gaps on the bottom of an igloo would be expensive and difficult for construction. In this method, natural ventilation is designed so that air in the gaps is replaced by air outside the igloo. This ventilation technique will enhance the thermal function and allow the igloo to better resist, avoid, or expel geothermal heat. And we conducted a simulation by maintaining the depth of an igloo at the current 27m and creating air gaps of 30cm in width and 2m in height surrounding the side walls. The result found that the occurrence rate of condensation declined 20% under the condition of dead calm. Finally, we conducted a simulation by creating air gaps of 50cm in width and 2m in height surrounding the side walls. The result found that the occurrence rate further declined by 40%.