Abstract: The objective of this study was to analyze the impacts of urban traffic on PM2.5 mass concentration. The cyclical characteristics and relevance at different scales between PM2.5 mass concentration and traffic flow were investigated based on the wavelet theory, which the data of 12 months from 2014 to 2015 in Beijing was adopted. In addition, the response lag time and reasons of PM2.5 mass concentration from traffic flow for special scales were researched. Results demonstrate that the PM2.5 mass concentration is closely related to traffic flow at daily cycle scales of about 24 hours, and the response lag time of PM2.5 mass concentration is about 9 hours.