On the top of the kiln, the fan has moisture exhaust system groups installed two sides, the moisture exhaust tube pass through the roof and strength to the air space, and there is a alumium butterfly valve installed in the middle of it. The moisture produced during the working process made the humidity of gas medium higher than the standard, then open the butterfly valve of moisture exhaust tube, let the moisture exhausted from the wind port of the fan, and suck the air from the inlet port, to achieve the moisture exhausted.