Based on the model from HT -HP rock experimental result and theoretical analysis, for epicenter area of strong and moderate earthquake, the properties and mechanical behaviors of rock deformation and failure under the condition of different temperature and pressure are studied. According to the model, during a loading circle, the small earthquakes move to the deeper crust gradually with the tectonic stress increases. The relocation results of some earthquake sequences support this concept model. Considering the mechanical behaviors of rock incremental failure and abrupt instability, the enhancement and quiescence phenomena of seismic activity before middle and strong earthquake, as well as the changing characteristics of b -value are studied primarily. The potential mechanism of two kinds of quiescence and change of b -value are discussed.