Urban dust pollution has posed adverse impacts on human's life and global climate. Accurate identification of the source and timely forecasting of dust pollution in urban area is crucial for developing mitigation strategies and protecting residents from air pollution. In this paper, the field observations were conducted and two theoretical models of dust passing model and point-source diffusion model were proposed to study the sources, propagation paths and forecast methods during urban dust pollution. The results show that the urban dust events can be categorized as external-source dusts and local-source dusts by the differences of developing processes, meteorological conditions and electrical natures. Then, combining the direction of horizontal wind speed and horizontal electric field with the topographic maps, we identify that the external-source dust originates from Badain Jaran Desert and Tengger Desert and propagates through the trumpet-shaped of terrain Qilian Mountains and the Helan Mountains to Lanzhou, which is in agreement with the result of HYSPLIT model. Whereas, the local-source dust is derived from the four bare ground areas located in upstream of the observation site and propagates along the Yellow River from northwest to southeast under the terrain condition that one river flow through two mountains. Finally, we suggest that external-source dusts can be forecasted by forward trajectory of HYSPLIT model and local-source dusts can be forecasted by establishing and monitoring anomalous changes of the threedimensional electric fields on bare ground in the upstream of the urban area.