The concept of “syndrome” is the core of TCM basic theory. This article reviews in terms of the concept and standardization of “syndrome” as well as syndrome differentiation methods. We lay special stress on expounding “syndrome” concept, standardization for diagnosing syndromes, its biological basis, and combination of macro syndrome differentiation with micro syndrome differentiation. Many experts have put a lot of energy to do research work, and made some achievements in above fields. But so far, the existing standardization of the syndrome has not yet been united, so there are still many problems to be solved about the specification of the syndrome. The authors also consider that we should pay attention to the study of biological basis of TCM syndrome in application of “omics” methods in the future.