By using meteorological observation data from eight weather stations in Southwest Guizhou and Micpas data and NCEP reanalysis data in recent five years， the spatial and temporal distribution of fog weather in Southwest Guizhou was analyzed in this paper． The results show that the main synoptic patterns resulted to fog weather here were the westerly flow in front of the southern trough and the northwest flow behind the upper trough，and physical quantity fields analysis indicated that the low － level air was wet when frontal fog appeared，and the atmosphere structure was relatively stable，there was a temperature inversion layer in lower level，and a weak upward motion nearby frontal area．