The frequent occurrence of regional air pollution makes it challenging to control. Based on source sensitivity research performed with the Chinese Unified Atmospheric Chemistry Environment (CUACE) model and dispersion simulation performed with the Flexible Particle dispersion model (FLEXPART), the regional transport of particulate matter (PM), potential source regions, and transport pathways were investigated for Beijing in summer (July) and winter (December) 2013. The mean near-surface trans-boundary contribution ratio (TBCR) of PM2.5 in Beijing was 53.4% and 36.1% in summer and winter 2013, respectively, and 51.8% and 35.1% for PM10. Regional transport in summer was more significant than that in winter. Seasonal difference of meteorological condition combined with the distribution of emission is responsible for seasonal difference of TBCR. The secondary aerosol is mostly contributed by regional transport. The transport of PM is mostly from Hebei province and Tianjin municipality. Based on backward trajectories analysis, the air mass source occurred from different directions in summer, while occurred from northwest in winter. The pollution level and the TBCR were closely related to the transport pathways and distance, especially in summer.