HAB(harmfulalgalbloom)isaseriousmarineecologicaldisaster.Uptonowthereisnodefiniteconclusionaboutitsmechanismofoccurrence.TheobservationresultsshowthattheHABbreakoutintheXiangshanBaywasmainlycausedbyphysicalconvergencecapacity,andthebreakoutprocesshadnodirectrelationtoeutrophication.AsanewideaitisthoughtthattheprocessoftheHABbreakoutismainlyaphysicalconvergenceoraccumulationprocessinsomeareas.AhypothesisaboutdynamicmechanismoftheHABappearingintheareaofftheChangjiangEstuaryisputforwardaccordingtohydrologyandtopographyandthepastwork,andabreakthroughisexpectedtobemadefordoingfurtherresearch.