Biochemicalmechanismofformingtheredtideisdiscussedinthispaper.Theexistenceofalargenumberofnitratesandphosphatesintheeutrophicwateristheprerequisiteofexplosiveincreaseofalgaeandtheformingofredtide.Reductionofeutrophicationisanimportantapproachtopreventingtheredtide.Themethodofdeeptreatmentofthewastewateranditsdenitrificationanddephosphorizationareintroduced,andanewopinionontheredtideformationandfundamentalpreventionisputforward.