On the basis of the data obtained by conventional observations, ground densified automatic weather stations (AWS), and NCEP 1°×1° reanalysis data, the synoptic causation of the sandstorm happening over Henan Province on March 27, 2006 was analyzed. The results show that the sandstorm occurred during the passage of a cold front. The upper air affecting synoptic system was a short wave trough which carried cold air, moved southeastward, developed and eventually substituted the former East Asia major trough. The deficient anterior precipitation resulted in the dryness of the surface. The Yellow River Flood Plain in North and East Henan Province provided abundant sand and dust to the occurrence of sandstorm. During the passage of cold front, the powerful temperature advection intensified wind power and vertical motion. The frontogenesis strengthened weather phenomena resulting from cold front. The cold front not only was the triggering system of static instability energy, but also had symmetrical instability inside which played an important role in the further enhancement of vertical motion and sending dust and sand to high levels. Mesoscale filtering of ground densified observations indicated that the formation and development of mesoscale low not only strengthened turbulent mixing, but also intensified the release of instability energy. The sandstorm was eventually formed by the effects of powerful wind, strong turbulent mixing and intensified upward air flow.