Abstract: A fan duct nozzle of an aviation turbofan engine. A notch is formed in a rear edge of an engine nacelle on an outer side of an engine pylon, and a flow guide curved surface matching the notch in shape is arranged on a profile of the fan duct nozzle. The notch is unilaterally formed in the outer side of the engine pylon, and a transition section between the notch and the rear edge of the engine nacelle includes two transition rounded corners. The present disclosure adopts a unilateral notch-shaped nozzle in the external duct of the turbofan engine, uses high-speed flowing of venting by an engine fan to provide flowing protection for an airfoil, improves a lift coefficient, and reduces negative impact on the airfoil exerted by the engine nacelle at a high incidence, thus lowering resistance, lowering a weight of the nacelle, and improving a lift-drag ratio.