Based on digital image technique,true sectional image of heterogeneous composite materials was obtained.By selecting local region of the section as individual cell for micromechanics characterization,local property field of material was acquired with the use of moving-window technique in sequence combined with improved FVDAM(finite volume direct averaging method),then local property field is used in FEM,loal stress is estimated in condition of macro-load,which presents a new way of thinking in analyzing failure of composite due to local behavior.