The strain rates in the different period during 1995-2005 in Beijing area indicate that the maximal shear strain rates, in the periods during 1995-1996 and 1996-1999, were larger than those in other periods and basically consistent with the period during 1996-1999 in which the seismic activity in Yinshan-Yanshan southern margin and Zhangjiakou-Bohai tectonic zones was high.

The relationship between M S 6 8 earthquake which occurred in Jiashi in February 2003 and the principal strain, superficial expansion and maximum shear strain are discussed and explained by mechanic theory.

Based on the principle of multiaxial critical plane approach, a multiaxial fatigue damage parameter was established, which takes account for the effect of not only the maximum shear strain amplitude and normal strain amplitude on the critical plane but also the parameter of non proportionality.

Based on deformation and failure behavior of the slope and an example, change laws of three variables(such as maximum equivalent shear strain-εqmax) with reduction coefficient Fsr during strength reduction are studied,and a new failure criterion is put forward by Fsr~εqmax curve.