Abstract: This paper discusses the current approaches of structuraldamage detection in structural health monitoring (SHM) and theirrespective features. The damage detection methods are classified into twocategories, one is based on the theory of modal analysis and another isbased on signal processing of the structural dynamic tests. The damage detectionmethod in the first category uses low order vibration modes of structure andrequires dynamic testing on the whole structure, the dynamic responsesof the structure can be calculated from its finite element model. In thesecond category, the damage detection method is usually used to detectdamage of structural components by the damage characteristic parametersextracted from measured dynamic response data without finite elementmodeling of the structure. The concepts of comparative method andnon-comparative method of damage detection are proposed in this paper. Inthe comparative damage detection method, the characteristic parameter of theintact structure is required to serve as the comparing template, while thenon-comparative method determines the damage state directly from themeasured dynamic response of the structure with the help of some physical andengineering knowledge. The problems of signal sensing and processingtechniques and the collocation of sensors used in damage detection are alsodiscussed in this paper. The approach to quantify damage severity and toestimate residual life of the damaged structure by combined activeand passive detecting techniques is proposed.