A sand-storm event occurred on the 6st April 2001 in North China is discussed. The results show, (1) the strong cold wave of the west Siberia and the surface warm and low pressure in southern Xinjiang and Mongolia offered the event dynamic and thermodynamic conditions, therefore the warmness and dryness made topsoil not been frozen, which provided lots of sand to the sandstorm weather. (2) The sandy weather caused serious accident of air pollution and made the air quality in Lanzhou even worse by 2 to 5 time. (3) The sand weather had positive and negative effect on the total solar radiation in Lanzhou. In the daytime, the sandy weather would diminish the absorbability of the surface net radiation and restrain the surface temperature. In the evening, it would diminish the emanation of the net radiation and restrain the surface temperature dropping.