After analyzing the development of the low-level jet stream associated with Baiu Front during the period from 24 to 25 June 1979, we discovered that its formation was closely connected with the upper jet stream at 300 mb and the low-level jet stream was developed in the area on the right-hand side of the entrance of the upper jet stream. According to the ageostrophic motions at the vicinity of an upper jet stream, there is a divergent region on the right-hand side of its entrance. This upper divergent regio...