A vehicle air duct assembly of an integrated beam structure includes a front beam member which is formed with an air vent duct for guiding air for the air conditioning of an automobile, a cowl cross bar for reinforcing the rigidity of the vehicle body and brackets for attaching a plurality of electrical equipment parts including an air bag; and a rear beam member which is coupled to the rear side of the front beam member and guides parts of air flowing through the air vent duct toward a front window glass of the automobile. According to the air duct, the number of parts is reduced, thus the manufacturing process is simplified, and a mixed material of steel and thermoplastic resin is used, thus the overall strength is increased and the weight is reduced.