From April 30 to May 5, 2001, Beijing experienced a continuous floating dust and heavy air pollution event. The main causes and the weather situation of the event are analyzed. The results show that a cold vortex at the upper level developed while moving eastward and a cold front on the surface moved across the dry and loose areas in the southern Mongolia and North China, thus resulted in the blowing dust or sand-dust storm. A large amount of fine dust particles moved to Beijing with the upper-level westerly flow and then floating dusts formed over Beijing. At the same time, Beijing was located at the convergence zone and had a stable stratification, small wind speed and frequent inversions in the weather charts. These were unfavorable to the local dust particle and pollutant diffusion; therefore, dust particles were gradually cumulated and heavy air pollution occurred.