With the aim to propose a reasonable and effective countermeasure for the elevated structure noise, the sound field radiated by a steel plate girder, which is the main source of the elevated structure noise, have been theoretically analysed. In the present study, steel plate girders are modelled as infinitely long elastic plate strips placed in parallel and numerical examples on the sound field radiated by the steel plate girders are shown. In the analysis of the radiated sound field, the equivalent source method is employed. Effect of the surface absorption on the sound field radiated by the girders is discussed through numerical examples. The results show that the surface absorption is effective for reduction of the radiated sound field, especially in the area that increase of sound pressure due to reflection by adjacent plate girders is observed. Furthermore, to design for reasonable countermeasure, variation of the noise reduction effect due to changing the pattern of surface absorption area on plate girders is classified.