The traffic vibration of bridge is not only harmful to the safety and durability of structures, but also hazardous to the ambient environment. Vibration of bridge is one of the most important sources of low-frequency noise. To improve the environmental quality in urban area, mitigating the noise and traffic vibration of bridge has become an important issue. In this paper, the vibration of a continuous steel bridge under traveling vehicle is measured. The wavelet transform method is used to analyze the vibration of the box girder and the deck of the bridge to investigate the characteristics of low-frequency noise. The present paper reveals that local vibration of the deck is the main source of low-frequency noise radiated from bridge vibration, which is almost independent of the running position of vehicle.