Allelopathic inhibition of cyanobacteria to other organisms is increasingly important among the multiple harmfulness of cyanobacterial bloom, and much attention has been drawn in ecology and environmental sciences in recent years. Many researches showed that the allelopathic inhibition has a wide variety of target organisms, including cyanobacterium and other algae, aquatic microorganisms, higher plants and animals. Over the past decades, the structure of pure allelopathic chemicals has been determined as phenol, alkaloid, peptide and terpenoid. The allelopathic inhibition of cyanobacterium to algae and aquatic microorganisms was mainly caused by inhibiting the photosynthesis. In some cases, inhibitory effects on the growth were tested in the presence of a proteinase. Temperature, nutrition condition, competition and genetic factor could also effect the allelopathic inhibition of cyanobacterium. By inhibiting the photosynthesis, cyanobacterium might be regarded as a nature herbicide. Although the previous studies about allelopathic inhibition of cyanobacterium well documented on the biochemical behavior of allelochemical and inducement of target organism to allelochemical, the release of allelochemical from cell and the immune mechanism of cyanobacteria to harmful allelochemical remained unclear and should be further emphasized. Several studies of the phenomenon, mechanism and condition of the allelopathic inhibition of cyanobacterium were also proposed in this paper.