Abstract: After No.9216 typhoon landed, it moved to the right entrance of the southwesterly jet at the 200 hPa level. A mesoscale rainstorm was generated and developed in the area far from the typhoon center. By using a 2-layer model, the process is analyzed and the positive feedback mechanism of the mesoscale storm rainfall with the coupling of low-level and upper-level jets and the typhoon circulation is studied. The results indicate that the Wave-CISK process and the symmetric instability of the baroclinic basic flow are the reasonable dynamic causes of the development of the low-level jet and the generation of the inverted trough. The baroclinic atmosphere with convective instability is advantageous to the development of instability of northward inertial gravity waves.