Abstract: Any material has its own properties and corresponding evolution laws,this is called the naturalcharacteristics of material.The mechanical behaviour of material is the results of interaction between its naturalcharacteristics and external conditions.Under some conditions,the external condition may cause biurcation to occurand make deformation process to show local non-determinancy. Sometimes the natural characteristics of materialca’t be obtained by traditional testing control metheds,which can only be obtained by adiusting testing controlvariables constantly according to the responses of material.