An effective numerical approach is proposed for structural damage analysis, especially for structures which may be damaged at multiple locations to different extents. The structural damage state is represented by defining a set of field-variable functions, and the degradation of material properties is described. Then, through customization of the commercial finite element software ABAQUS/Standard, the damage state is directly assigned to the integration points of elements, thereby avoiding modification of the finite element model. Afterwards, the damaged structures by ABAQUS/Standard is conducted numerically. Finally, this approach is verified by simulating the growth of delamination for a pre-delaminated composite plate and a composite plate under impact loading, respectively.