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The climate characteristics of dense fogs and the anomalous circulation characteristics and atmospheric circulation patterns of autumn dense fogs since 2000 in Heilongjiang Province are discussed. This research shows that dense fog days appear mostly in summer in mountain areas. The dense fog events causing severe disasters with wide range and long duration occur most frequently in autumn. All the persistent dense fog weather events in October and November are after 2010 Most of the dense fog days occur under the warm and the moist background in autumn. Based on the 500 hPa mean height and anomaly fields, the major atmospheric circulation patterns, the lower height in west and the higher height in east and the zonal circulations are put forward. Anomalous circulation characteristics such as the big positive height anomaly at middle and lower levels, anticyclone circulation at 850 hPa, and the strong norththannormal Northwest Pacific Subtropical High are helpful to improve the quality of fog forecast in the medium and short term in Heilongjiang Province.