Meteorological dust storm frequency data from 37 stations of 40 years (1961--2000) throughout the Midwest Inner Mongolia of China are analyzed together with climatic factors of 40 years in this region. Dust storm frequency in this region has taken on a decline trend during the period of 1961--2000. The main climatic factors controlling dust storm frequency in this region are number of days with gale, intensity index of Asian polar vortex, and area index of the northern hemispheric polar vortex which are good representatives for large-scale cold air activities. The explanation for the decreasing trend is that it is mainly due to the variation in climatic factors determining dust storm frequency in Inner Mongolia of China.