A sealing mechanism for an air-conditioning apparatus includes a fixed portion having an opening and a limiting rail; and a moving portion connected with the limiting rail and movable along the limiting rail to close or open the opening. At least one of the fixed portion and the moving portion is provided with a first sealing protrusion, and the first sealing protrusion is arranged between the fixed portion and the moving portion. The sealing mechanism may be used with a ventilation assembly of the air-conditioning apparatus.