Abstract: A special form of air pollution called fumigation with mountain-valley wind shift is first distinguished based on air pollution monitoring data in Dukou city.This kind of air pollution occurs frequently in spring,autumn,and is specially serious in winter season.A model of fumigation accompanaying shift from mountain to vally wind is developed to investigate the observed facts.It is demonstrated that the model provides not only the accurate predictions of the values of high concentration at ground level but also the times and locations of occurence.Ground level concentration of SO2 in above stated case is several to ten or more times stronger than 24-hour means in that area.It is one of the most important processes of air pollution in Dukou city.The model might provide useful guidance for the researches on air quality prediction and control measures.