Abstract:With conventional meteorological data as well as NCEP/NCAR reanalysis data, the processes of the typhoon 9711 and the typhoon Matsa (0509) are diagno sed and compared.　The result indicates that the re strengthening of the typhoo n 9711 after its denaturing was due to intense development of a frontal cyclon e, which was incarnated by downwards moving of the upper level potiential votici ty, the tropical low pressure circulation and the low level front. But in the p r ocess of the denaturing of the typhoon Matsa, there was no low level front, and the atmospheric slanting piezotropy was weaker. So the mutual influence of downw ards moving of the upper level potiential voticity, the tropical low pressure c irculation and the low level front did not exist. MPV1<0 and MPV2>0 were characteristic storm rainfall area, which is a good denotation of this kind of rainstorm. Downwards moving of the upper level potiential votic ity is advantageous to releasing of the unstable energy, and causing the increas ing precipitation.