To analyze the main sources of low frequency noise in highspeed trains, the structural vibration and acoustic radiation theory was used to study the relationship between the characteristics of the sound field in the vehicle and the vibration of the interior plates. The experimental results show that the vibration of the interior plate and the coupling response characteristic of the sound field in the vehicle are universally applicable in the process of acoustic and structural sound propagation. This method is applied to analyze the noise characteristics of a highspeed train under different speed levels, open lines and tunnel conditions. The results show that, the higher the running speed of the train, the more significant the amplitude of the low frequency vibration of the interior panel increases, which leads to the peak of the low frequency noise in the car. Under 350km?h-1 operating conditions, the low frequency noise peak mainly originates from the floor vibration and the increase of the noise in the tunnel environment is due to the sidewalls and ceilings acoustic radiation. The contribution of each panel was quantified. Finally, the operational transfer path analysis (OTPA) method was used to quantitatively calculate the noise contribution of noise sources. The results show that the aerodynamic noise proportion is the largest, but the sum total of vibration excitation of 60%, especially at the peak frequency of 160 Hz, the contribution of the cooling fan vibration is the largest.