The latest development of APE theory for anisotropy study is introduced and applied in electric problem s.In the view of APE cracks modeling,it is believed that when there is no newly developed cracks,the dilatancy and closing of cracks balance each other.Using a new electric conductivity anisotropic model (named cubic model),put forward by present authors,for the cracked rocks containing fluid,the mechanism of earth resistivity precursor of earthquake is discussed according to the APE theory,considering the variation of aspect ratio to be the main source of the precursor due to stress change.It is concluded that the increasing or decreasing variation of earth resistivity with large amplitude before strong earthquakes could be explained easily by the new electric anisotropic model,even if the total porosity or strain do not change or there are no new cracks developed.Moreover,it is found that resistivity variation characteristics are related to the aspect ratio and distribution of cracks.But the conclusions from the discussion in this paper are effective only for seismic field precursor,not for source precursor related to new developed cracks.