Abstract: Based on surface air pollutant monitoring data,conventional meteorological data,the Europe Center for Medium Range Weather Forecast (ECMWF) reanalysis data and the L-band radiosonde observations,a heavy dust pollution event occurred in the Yangtze River Delta on May 5-7,2017 was analyzed in the combination of using a backward trajectory model.The results show that this dust pollution event is influenced by the weather system,surface meteorological factors,and boundary layer conditions.The eastward movement of East Asian rough,the southward movement of cold air,as well as the development of high pressure at surface lead to the occurrence of dust weather in the Hexi Corridor region,most of Ningxia Hui Autonomous Region and the western Inner Mongolia,which provide dust source for dust transport to the Yangtze River Delta region.Strong winds at 850 hPa favor the transport of dust particles from the upstream dust source region to downstream region.The descending movement of air at the high-pressure center and the enhancing convection in the daytime provide dynamic conditions for the effect of dust at high altitudes to the surface.As dust particles arrive in the Yangtze River Delta,cold air becomes weak and the near-surface layer remains stable,which is unfavorable for the pollutant dispersion and results in the heavy pollution event.