Using the upperair and surface observation data and sandstorm instrumental data of Inner Mongolian sandstorm monitoring stations, a severe sandstorm which lasted in the period from 19 Jan to 20 Jan 2010 was observed and analyzed. The result show that: Before the occurrence of this sandstorm, the stability of atmosphere was not conducive to the development of convection. However, the difference advection between from 700 hPa to 500 hPa and below 850 hPa was favorable for the increasing of temperature lapse rate. The strong cold advection caused a thermal convective instability which formed at the levels below its center and was favorable for the sandstorm burst. When dryconvective storm started and led to a sandstorm, the instable energy was released, which made the layer of the atmosphere tends to be a neutral stratification, namely the mixed layer. This layer may be an equilibrium state during the whole process. To some extent, the strength, location, and level of the cold advection in the middle and lower troposphere influenced the thickness of the mixed layer and the intensity of the sandstorm. During the process, due to both of the quick droppings of the temperature in the layers below the mixed layer and the heating effect of shortwave radiation at the top of sandstorm, there formed a temperature inversion cap at the top of the mixed layer (about 500 hPa). The strong cold air activity was the main reason for sandstorm occurrence which accompanied by the sharp dropping of land surface temperature and relative humidity, as well as by the rising of air pressure. The surface wind speed directly affected the strength of sandstorm. PM10(inhalable particle matter) value can reflect and describe the change of the sandstorm intensity in a better level. The change trend of the particles scattering coefficient was highly consistent with PM10 value: During the sandstorm, the scattering coefficient was generally above 1000 Mm-1; while the sandstorm being a strong one, it was mainly above 2000 Mm-1.