The invention provides an air conditioner indoor unit and a fresh air ventilating control method thereof. A fresh air device is arranged on one side of the indoor unit and used for conveying outdoor fresh air into the indoor space. The fresh air ventilating control method comprises the steps that the indoor unit starts a refrigerating mode; the indoor air quality value is obtained; whether the indoor air quality value is larger than the first preset air quality value or not is judged; if yes, the fresh air device is started to operate at the first ventilating rotating speed to conduct fresh air ventilating; the indoor air quality value is obtained again; whether the indoor air quality value is smaller than or equal to the first preset air quality value and larger than the second preset airquality value or not is judged; if yes, the fresh air device operates at the second ventilating rotating speed to conduct fresh air ventilating; and the fresh air device stops operating till the indoor air quality value is smaller than or equal to the second preset air quality value. According to the air conditioner indoor unit and the fresh air ventilating control method thereof, the indoor airquality can be controlled while the indoor temperature is stably controlled, and the good experience is provided for users.