Abstract: An ecological survey was carried out in May and September 2014 in the Laizhou bay, with the aim of exploring temporal and spatial variations of phytoplankton community and their correlation with environmental factors. The results showed that differences of the average salinity, concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphate (DIP) in the two months were not obvious, with the differences of 0.80, 4.90 μmol/L and 0.01 μmol/L, respectively. Compared to the values in May, the average of temperature and dissolved silicate (DSi) concentrations increased 11.0℃ and 6.02 μmol/L, and declined gradually from the inshore to offshore waters in September, corresponding to the increased freshwater loading. The analysis of nutrient structure indicated that no sites appeared nitrogen limitation in two surveys. Up to 80% sites showed absolute and relative limitation in DSi, while DIP limitation only appeared in one sites in May. In contrast, 86.7% of the sites had DIP limitation but only one site had DSi limitation in September. The reason might be related to increased precipitation and silicate loadings during the water and sediment regulation of Yellow River in July. Phytoplankton responded to environmental changes and higher diversity and biomass of phytoplankton appeared in September. The results of Canonical Correspondence Analysis between phytoplankton assemblages and environmental factors indicated that increased temperature and concentrations of DSi were dominant factors related to the temporal and spatial variation of phytoplankton. Dinoflagellates had a higher sensitivity to changes of temperature and salinity than diatoms.