Based on the investigation of 18 Clear Air Turbulences (CAT) reported by the ai rcrafts in the area of Beijing Air Traffic Control Center during 2005 to 2008,4 sorts of CAT were classified according the atmosphere circulation. They were JET , trough, ridge and shear line. Combining the satellite images analysis, the fea tures of each sort of CAT and the method of CAT forecast were concluded. At last , a case of CAT was studied and the results showed that the edge of the upper je t stream, the wind shear and large temperature gradient were easier to produce CAT.