Abstract: On the basis of phytoplankton and environmental ecological investigation in Luan Estuary-Dapu Estuary in spring and summer. There are 3 phylum 15 families 44 species of phytoplankton were identified, diatoms was the most and accounted for 85%.Species number in summer was significantly higher than that in spring. The obvious seasonal succession was found based on the Jaccard with 0.14.There were 3 dominant species in total, Noctiluca scientillans、Rhizosolenia alata was the dominant species in spring, Skeletonema costatum was that in summer. Because of dominant species was simply and dominance was high,the community structure was instability. The number of phytoplankton ranged from 1.14104/m3 to 827.73104/m3 with the descending order from offshore areas to pelagic sea and The rangeability was summer greater than spring. The average number of the summer was 7 times than spring. The Shannon-Wiener's index H', Margalef's richness index dMa and Pielou's evenness index J all reflect that Summer habitat conditions better than the spring, Luan Estuary better than Dapu Estuary. No significant relationship between phytoplankton and single environmental factor in spring .temperature was the major limit factor for the number of species and cells number in summer and salinity was major acted on species number,little correlation with cells number,what's more,DIP was the main limit factor for cells number but little correlation with species number.