The teleseismic waveforms of the MW7.6 September 20, 1999 Chi-Chi earthquake were examined to obtain the quick information on the fault rupture process. The deconvolution results show the fault ruptured from south to the north, and revealed the west movement of the hanging wall to the footwall on the eastern dipping plane. The spatial slip distribution shows that the earthquake was mainly composed by a large asperity with a dimension of about 45km × 15km. The maximum slip was about 8 m located at about 45 km to the north of the epicenter. The slip distributions obtained in this study have a good agreement with the observed surface breaks. The comparable static and the dynamic stress drops of about 11 Mpa in the large slip region indicate that the melting/fluid pressurization might have taken place in this earthquake. It reduces the dynamic friction and results in the large slip observed.