Abstract: Abstact: Terrestrial nitrogen input plays an important role in the phytoplankton ecosystem of coastal waters. To understand the response of the phytoplankton of Jiaozhou bay to the input of different nitrogen sources, an on-site enrichment experiment was carried out in coastal water of Qingdao in the autumn of 2020. The effects of enrichment culture of different nitrogen sources on phytoplankton community structure in Jiaozhou bay were analyzed by microscope and CHEMTAX method. The promoting effect of single nitrogen source on phytoplankton cell growth was CH₄N₂O>NH₄Cl>NaNO₃. The compound nitrogen source in Licun river significantly promoted the growth of phytoplankton (P<0.01). After enrichment culture of nitrogen source, the dominant species will evolve from Pyrrophyta to Bacillariophyta. The results of microscopic examination and CHEMTAX showed that there was a very significant positive correlation between Pyrrophyta cell abundance and Chl a biomass (r=0.656, P<0.01) and there was a significant positive correlation between Bacillariophyta cell abundance and Chl a biomass (r=0.674, P<0.01) in different nitrogen source culture systems; The utilization rate of phytoplankton to DON is greater than DIN, and the utilization rate of compound nitrogen source is greater than that of single nitrogen source. This study clarified the effects of several typical nitrogen source inputs on the dominant species of phytoplankton in Jiaozhou bay, provides a theoretical reference for the development and utilization of marine biological resources, and provides a theoretical basis for the protection of marine ecological environment in coastal waters.