Abstract: Currently, many nomenclatures have been given as the name of active organic matter, (such as Labile Organic Matter, Microbial Biomass Organic Matter，Light Fraction Organic Matter, Dissolved Organic Matter, Particulate Organic Matter) and no unified definition has been established yet, as disparate angles and methods are adopted by different researchers, which triggers confusion in understanding. In this passage the sources of these nomenclatures, definitions and their relationships with soil nutrients were all clearly addressed in a systematic way, and thus can be of some help in better understanding the knowledge about active organic matter, revealing the correlations between the relative indexes, and clarifying some concepts as well.