Abstract:Using conventional observational data ,satellite images, Dopper radar echo and NECP data, the causality of the strong convective severe sand dust storm in the south of Hebei on May 10,2005 is discussed. The results show that the v ertical structure of cold advection in the upper air and the warm advection in t he lower level, and increasing temperature at afternoon provided the advantageou s thermal condition. Strong surface winds were mainly caused by a squall line ah ead of the cold front which showed as a arc echo, the surface mesoscale converge nce line is very important to the squall line. Meanwhile, the development of upp er level jet and strong downward transport of momentum by the sinking branch o f the upper level jet's secondary circulation are also important for the formatio n of strong surface winds. The dust devil occurred at the coupled area of high/l ow level jets and the superposition of the positive helicity value at 700hPa and high energy tongue and the higher gradient of the helicity's positive value at 300hPa, the magnitude of the tropospheric helicity is useful for the prediction of dust devil events.