The invention provides a using method of a fresh air source device. The fresh air source device comprises a haze absorption device, a rotary filter valve, a haze cleaning device, an air compressor, a fresh air storage tank and a heat pump device. When the fresh air source device is used, a controller controls a condenser of the heat pump device to supply a heat source for the haze absorption device and a cooling source for the haze cleaning device; the haze absorption device utilizes a water pump and the heat source to generate water fog and steam to sterilize and disinfect air, the haze cleaning device utilizes the cooling source to cool the water fog and the steam into water, a filter is utilized to filter and reuse the water, and thus clean fresh air is prepared.