The invention discloses an air inlet channel applied to a fresh air purification system. The air inlet channel is arranged at an air inlet end of the fresh air purification system, and comprises an internal circulation air duct and a fresh air duct; an air inlet end of the internal circulation air duct communicates with indoor air, while an air inlet end of the fresh air duct communicates with external atmosphere; a switching mechanism for closing or opening the fresh air duct is arranged in the fresh air duct. The air inlet channel of the present invention enables the fresh air purification system to have two modes, namely internal circulation purification for removing smoke, particulates, dust and the like in indoor air as well as thermal insulation, and fresh air intake for oxygen enrichment, ventilation, odor removal, moisture removal, room temperature regulation and the like; by means of switching of the internal circulation purification and the fresh air intake, the working efficiency of the fresh air purification system can be improved, and the energy consumption is relatively low, especially obvious in winter; the switching mechanism is ingenious in design and convenient and fast to operate; furthermore, the air inlet channel is simple in overall structure, convenient to produce and manufacture, and low in cost.