Five sampling sections were set in the Kunshan area of Dianshan Lake to study the ecological status of plankton after the complete removal of aquaculture net in spring 2008. The results showed that the temperature at different sampling sites of Kunshan area of Dianshan Lake wasn’t different. pH value was between 8.39 to 8.85. The conductivity value was 0.87-1.02 μs/cm. The dissolved oxygen was 8.92-12.71 mg/L. The value of transparency was very low,at 0.35-0.60 m. TN was all higher than 3 mg/L. TP was 0.11-0.57 mg/L. The concentrations of heavy metals were very low. In the study,phytoplankton was found 8 phylum 215 species,and the average density was 2.119×10⁷ ind/L. Rotifer was found 9 families 30 species,the dominant specie for the rotifer was Polyarthra trigla. Cladoceran was identified 8 genus 10 species,dominant specie was Bosmina coregoni. Copepod was identified 8 genus 10 species,dominant specie was Mesocyclops leuckarti. The results showed that the Kunshan Dianshan Lake was already eutrophic,in other words,after dismantling the aquaculture net,we must strengthen the water quality management,and there is no time to lose in ecological control and governance.