Abstract: According to the water quality survey data collected from the scallop culture area in Zhaoyuan coastal waters of Laizhou Bay from May to November during 2015−2017, we analyzed the spatial distribution, community structure and interannual variation characteristics of phytoplankton. The study identified 138 species of phytoplankton, among which 86 species were Bacillariophyta, that was dominant in respects of both quantity and species composition. The phytoplankton density, biodiversity index and evenness index showed obvious seasonal characteristics. Phytoplankton density were the highest in May−June and September−October. The biodiversity index ranged from 1.92−3.57, and the evenness index variation ranged from 0.44−0.87. Phytoplankton was mainly in temperate coastal ecological type and the community structure presented temperate floristic characteristics of sea area. There were many species of phytoplankton which distributed rather evenly, and the community structure was relatively stable.