For the modern large commercial aircrafts, during the phases of approach and landing, when the engines are at low operate with the high-lift devices and landing gears all deployed, the airframe noise, the majority of the aircraft total noise, is notable. Over the last decades, a considerable amount of work has been conducted on the noise characteristics, noise mechanism, noise reduction techniques for the high-lift device noise. The high-lift device noise is generally categorized into three parts, low-frequency tones generated from the slat cove, mid-frequency broadband noise generated from flap side edge, and high-frequency tones generated from the slat trailing edge. The noise reduction techniques have active and passive flow control and noise reduction methods, such as slat cove cover, slat cove filler, droop nose and blowing-suction air, plasma actuation, etc.