The invention relates to an internal rotation type window seam ventilation installation method of a purification fresh air ventilator. The method is applied according to the steps that a window is opened firstly, a window sealing plate 1 is in sealed connection with a window frame 4, a fresh air ventilator air opening is connected with a vent pipe installation disc 2 through a vent pipe, the window is rotated in the closing direction until the vent pipe is not pressed by the window, and therefore outdoor air is conveyed to the purification fresh air ventilator through a vent hole 3 and the vent pipe; or air in the purification fresh air ventilator is conveyed to the outdoor place through the vent pipe and the vent hole 3. After the method is applied, fresh air purification and ventilation are effectively carried out through the vent pipe penetrating a seam of the opened window, the purification fresh air ventilator is installed, the indoor PM2.5 index is in the senior level all the time after the purification fresh air ventilator is started by one hour, haze harms are effectively prevented, and the resident health level increase is promoted; in addition, 200 Yuan of installation and punching cost can be saved from each purification fresh air ventilator, and the installation and punching cost accounts for more than 65% of installation cost; and in addition, equipment installation is silent and does not disturb residents.