The invention provides an air duct assembly for supplying air to a compartment. The air duct assembly comprises an outer casing and an inner casing, wherein the outer casing is configured to be fixedon the outer side of a compartment plate wall defining the compartment, and an outer accommodating cavity is defined in the outer casing; the inner casing is configured to be disposed on the inner side of the compartment plate wall opposite to the outer casing, and an inner accommodating cavity is defined inside the inner casing; the outer casing is provided with an air inlet to allow external airto enter the outer accommodating cavity through the air inlet; a ventilation opening is formed in the compartment plate wall to enable the outer accommodating cavity to communicated with the inner accommodating cavity; and an air outlet is formed in the inner casing to supply air in the inner accommodating cavity to the interior of the compartment. The air duct assembly does not need to be attached to an additional auxiliary structure, can be conveniently and quickly installed on any plate body provided with air flow holes, and can be further installed at any position of any compartment alongwith the plate body and supply external air flow for the compartment.