In recent years many articles state that jellyfish populations have been increasing worldwide in global oceans. Jellyfish blooms have been one of the marine ecological disasters that have many negative effects on marine eco-environments and human activity and eventually damage the normal composition and function of marine ecosystems. Jellyfish decomposition is associated with the end of jelly-blooms, and it also plays an important role in marine ecosystems and has enormous influence on the ecological environments. However, previous studies have paid less attention to jellyfish decomposition as compared with jellyfish blooms, so research on the effects of jellyfish decomposition on marine ecological environments is of great significance. We compile and discuss the existing evidence on decomposition of jellyfish blooms, the strategic and observational oceanographic techniques of monitoring jellyfish fall and decomposition, the sinking rate of jellyfish corpses and the factors that influence jellyfish fall and decomposition. The influence of jellyfish decomposition on biogenic elements, dissolved oxygen, seawater acidity, and the marine biological community is analyzed. The relationship between the increase of jellyfish biomass and the marine ecosystem is preliminarily assessed. Compiling and analyzing the existing results of the research on jellyfish decomposition, we conclude that the processes of jellyfish decomposition are fast, transitory, and persistent. Decomposition speed was mainly influenced by sinking speed and decay coefficients. Jellyfish sank between 850 and 1500 m/d on average, and decay coefficients varied from 0.67 to 1.12 d^-1. The mean release rate of dissolved organic carbon (DOC) of dead jellyfish was 0.36 mg g^-1 d^-1. The efflux of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) was (7182 ± 2934) μmol m^-2 h^-1 and (725 ± 124) μmol m^-2 h^-1 respectively,while the efflux of NH₄⁺ and PO₄^3- reached (2044 ± 519) μmol m^-2 h^-1 and (287 ± 47) μmol m^-2 h^-1 respectively. As jellyfish decomposed, the ambient water environment became acidic and hypoxic and even anoxic. The pH of water decreased by 1.3, and the dissolved oxygen demand reached 65.5 μmol kg^-1 h^-1 on average. These results further suggest dead jellyfish are a valuable source of biogenic elements that directly influence the cycles and biogeochemical processes of biogenic elements. Dead jellyfish can be consumed by mini- and micro-scavengers and returned to the faunal food web to compensate for the reduced energy. Dissolved organic matter leaching from dead jellyfish fuels other microbial communities and enters the microbial loop, which can influence distribution and biomass of microbial communities. Furthermore, the large amount of biogenic elements from aggregations of dead jellyfish may cause secondary ecological disasters, such as red and green tides. Additionally, decomposition of jellyfish blooms can cause seawater acidification and low dissolved oxygen and finally lead to acidic and hypoxic or anoxic conditions, which may induce mass mortality in other marine organism. Overall, decomposition of jellyfish blooms has tremendous influence on marine environments. Basic information on mechanisms of jellyfish decomposition is still unknown, so further investigation is worthwhile. We summarized the existing evidence on jellyfish decomposition and the sinking of dead jellyfish and discussed the influence of jellyfish decomposition on the marine ecosystem to provide basic data for studying the mechanisms of jellyfish blooms and decomposition.