An air outlet device, an air conditioning system, and a control method therefor. The air outlet device is for use in an air conditioning system, and includes: an air outlet device for an air conditioning system, including: a heat exchanger that exchanges heat with the air flowing through; a fan device that drives the air to flow through the heat exchanger; a formaldehyde removal part coated with a formaldehyde removal coating that can catalyze the decomposition of formaldehyde into water and carbon dioxide; a housing for accommodating the heat exchanger, the fan device, and the formaldehyde removal part; and a controller for controlling the start and stop of the fan device. According to the air outlet device, the air conditioning system, and the control method therefor of the present application, the air is purified by providing a formaldehyde removal part in the housing of the air outlet device.