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.