Abstract: Observational study and numerical simulation were conducted on a severe dust storm process induced by the intensive development of Mongolia cyclone occurred from 6 to 8 April 2001 in Inner Mongolia. The results showed that the cyclonic cold front in this "cyclonic dust storm" process was the direct and important portion of cyclonic system inducing the dust storm. Because the cyclonic cold front (associated with strong surface wind, strong frontal raising, etc) is favorable for the formation of severe dust storm and so often accords with it. The strong surface wind, which associated with the dust storm strength closely, was mainly caused by the rapid cyclogenesis and the cold advection. Meanwhile, the great downward transporting momentum was another reason that contributed to the formation of strong surface wind. In west Inner Mongolia, the great momentum at upper troposphere was firstly transported to middle troposphere by the descending branch of the upper level jet's secondary circulation, but under it the downward transportation was not notable because the mixed layer (ML) was shallow. In contrast, in the middle-north part of Inner Mongolia, the great momentum was downward transported to middle troposphere because of the development and drop of the upper level jet. In lower troposphere, a deep ML formed there and so transported the great momentum from mid-lower troposphere down to the surface. It was the important reason that the "black st orm" accrued there. The ML is the crucial stratification factor affecting the formation of dust storm because it can minimize the energy requiring to develop the deep dry convection and so is favorable for the formation of dust storm. It's depth and strength mostly determined the strength of dust storm. In this case another reason that the black storm occurred in the middle-north part of Inner Mongolia was the formation of deep ML, which was induced by the surface heating for a long time. The advection of the ML air also contributed to the formation of deep ML there. So, the deep dry convection can developed when the cold front passed and the severe duststorm occurred there. The sensitivity experiment proved that the surface heating was the crucial factor affecting the dust storm in this case. Firstly, it was the main forcing factor of the cold frontogenesis. Secondly, it induced the deep prefrontal ML developing at middle-north part of Inner Mongolia. Thirdly, it influenced the strength of surface wind by affecting the downward momentum transportation in lower troposphere.