By using the data from AWS stations, radar observations, reanalysed data of NCEP 1°×1°, adopting the relative coordinate system with Matsa moving, a case study is made of the abnormal rainstorm process for typhoon Matsa in August 2005. The results indicate: (1) The structure of typhoon Matsa is quite different from common typhoons, and the unusual distribution of rainfall is closely related with the special situation. (2) There was a number of rain clusters reproduced and moved in the first and second quadrant of the typhoon system, which were corresponding to the areas where there were strongweak interweaved radar echoes for updrafts and downdrafts occurred alternately; the frequent appearing and movement of mesoscale “rain cells” were key mechanisms for the generation of the severe rainstorm. (3) The areas where local unusual variability occurred due to special structure changes in certain quadrants of the typhoon system can be a significant indicator for the monitoring and forecasting of typhoon heavy rainfall.