Aiming at the problem of radiated noise in automobile transmission housing, a method to find the exact location of effective reinforced concrete parts by using modal acoustic contribution analysis and panel acoustic contribution analysis is proposed. In this paper, the sound pressure curve and its peak frequency of the transmission shell are obtained by using the analysis method of acoustic boundary element. Then, by analyzing the contribution of modal acoustics at peak frequency, the modal order of the larger contribution to the noise is obtained, and the local area with large acoustic contribution is obtained from the modal cloud. Finally, the localized region of the acoustic contribution is analyzed by the acoustic section contribution analysis, so as to find out the acoustic Contribution to the larger and need to improve the specific parts. Furthermore, the structure of the transmission case is improved, and the improved structure is verified. The study shows that the method of reducing the radiation noise of the shell by means of modal acoustic contribution analysis and panel acoustic contribution analysis is an effective method to find out the specific parts of the shell that need to be improved intuitively and accurately, and the improved shell structure can be effective improved the noise characteristics of the shell.