Background: Environment DNA obtained from environment samples,such as water,soil and so on.DNA release from exfoliated cells、 urine、 feces of biology or after biological death released.eDNA was released into the environment that can persist in a certain period.Environment DNA is exist by DNA molecule free dissolution or in combination with other substances.Compared with traditional species monitoring techniques,eDNA species monitoring technique is a non-invasive method and have no harm to species.Under the situation of high-sequencing rapid development,multiple-species eDNA approach by DNA metabarcoding for simultaneous molecular identification of multiple taxa in a complex sample has applied in the investigation of freshwater ecosystem.Environment DNA has been used to estimate the presence/absence of species.Studies have reported species biomass have a positive relative with species eDNA concentration.