The dynamic rupture process of the Chi-Chi earthquake has been investigated based on a 3-D spontaneous shear crack model, using a thick fault zone model and a slip-weakening friction law. Our results show that the dynamic rupture process of this event is very complex. The distribution of the rupture starting time is much more inhomogeneous than that of the kinematic model. We find that the zones with a large strength excess on the fault surface delay the rupture propagation. The rupture front jumps from the zones with high strength excess to the near zones with low strength excess when encounters the zones with high strength excess, leaving the unbroken zones behind which subsequently rupture. We also found that the motion on the hanging-wall side is larger than that on the foot-wall side.