Abstract: Taking a rail transit vehicle as the research object, the noise excitation source is investigated. Based on the geometric ray acoustics method, a prediction model of exterior noise is established. Then, the investigation result of main noise sources is taken as the input, the quantitative relationship of the excitation source influence on metro train exterior radiation noise is analyzed. The results show that the train exterior radiation noise is significantly affected by wheel-rail noise, every 1 dB(A) increase of which will cause 0.9~1 dBA increase of the radiation noise. The next biggest noise impact comes from the gear box and traction motor, while pantograph noise has the least influence.