By installing sound pressure sensors on the surface of the test aircraft, the noise load on the surface of the aircraft during flight was measured. The aircraft surface noise load measured during flight testing is mainly composed of engine noise and turbulent boundary layer noise. These two types of noise usually have different transmission efficiencies when propagating into the cabin. Attempt to separate the engine fan inlet noise from the total noise by utilizing the coherence difference between turbulent boundary layer noise and engine noise between sensors. Sound pressure level of total noise load and engine noise on the surface of aircraft is obtained during takeoff, climb, and cruise. By comparing the noise levels of aircraft during takeoff, climb, and cruise, analyze the variation patterns of engine inlet noise on the aircraft surface during flight. The results show that when the corrected speed of the engine is the same, as the altitude and speed of the aircraft increase, the BPF noise on the surface of the aircraft gradually decreases, and the broadband noise gradually increases. The total sound pressure level of engine noise on the front side of an aircraft is highest during constant climb, followed by cruise control, and lowest during takeoff.