Based on the new generation weather radar (CINRAD/SC) data ， Micaps data，Auto-station observation data and MM5 products ，a squall line gale process with disaster gale，weak precipitation and local hail occurred in Linyi on April 28， 2006 is analyzed.The result shows that the weather dynamic mechanism of the “Apr.28” squall line is ：the disaster gale happened in left side of high jet (HJ)，where is the area of positive vorticity advection and divergence，strong vertical wind shear leads to the MGW and the MGW is the mechanism of the “Apr.28” squall line. Strong sinking motion comes from the dry and cold air at middle level.Radar observation indicates：characteristics of this process are original radial velocity，radical wind convergence ，less VIL，boundary weak echo and middle level radial convergence etc.The fast decrease of negative radial velocity centre value at the upper level as well as its prompt increase at lower level are attributed to the fast sinking of downward flow at upper level,the result is disaster gale on the surface.