Through the investigation on the enclosure phytoplankton community in pearl mussel ponds,we comparatively studied the different effects of silver carp(Hypophthalmichthys molitrix),bighead carp(Aristichthys nobilis)and the pearl mussel Hyriopsis cumingii on quantity,biomass and dominant species of phytoplankton,and the effects of the two carps on the phytoplankton in mussel ponds.The results showed that the density and biomass of phytoplankton in mussel monocultured pond(10#)are significantly higher than those in high density of silver carp monocultured pond(12#)(P<0.05),the density and biomass of cyanobacteria in mussel pond is significantly higher than those in high density silver carp pond(12#)and low density bighead carp pond(13#)(P<0.05),the density of chlorophyta in mussel pond is significantly lower than that in low density silver carp pond(11#)(P<0.05).The density of phytoplankton in mussel culturing pond(10#)is significantly higher than that in low density of silver carp coculturing pond(15#,16#)and bighead carp pond(17#,18#)(P<0.05),the density and biomass of cyanobacteria in mussel pond is significantly higher than that in silver carp pond(15#,16#)and bighead carp pond(17#,18#)(P<0.01),the density of chlorophyta in mussel pond is significantly lower than that in high density silver carp pond(16#)and low density bighead carp pond(17#).The impact on phytoplankton among mussel,silver carp and bighead carp is different from each other.The introduction of bighead carp or silver carp to enclosures of H.cumingii could effectually control algae especially Cyanobacteria(Microcystic aeruginosa)and promote the growth of Chlorophyta(Scenedesmus quadricauda)and finally help pearl mussel culture.The density and biomass of phytoplankton all decreased along with the increased density of silver carp while the increased density of bighead carp promoted the growth of Euglenophyta (Euglena viridis).