Single-directional fresh air system, also known as forced exhaust and natural supply ventilation system. For example, in residential settings: exhaust outlets are installed in areas with accumulated polluted air, such as kitchens and bathrooms, directly connected to the vertical shaft of the bathroom or the flue of the kitchen. The air intake for fresh air is installed above the doors and windows in bedrooms and living rooms, directly connecting to the outdoors. While the system is running, indoor air is continuously exhausted to the outside through the exhaust outlets, creating a negative pressure inside. Fresh air is then filtered, dehumidified, deodorized, and noise-reduced before being continuously supplied into the room for 24 hours.