Abstract: Based on the conventional observation data from automatic weather station and NCEP reanalysis data, the vertical helicity of a severe sandstorm occurred on Mar 19th in 2010 over the middle west region of Inner Mongolia was diagnostically analyzed. The results showed that during the sandstorm the helieity, an obvious ＂negative above positive below＂ structure was observed, and this structure appeared at the same time as strong sandstorm occurred. Following the range extension and height elevated of positive helicity, the sandstorm gradually became stronger. The corresponding relation between the evolution of negative helicity at high level and appearance of the sandstorm was also observed in this study. Diagnostic analysis might be helpful for the dust storms forecast.