In this paper, structural equation model (SEM) is used to explore the inﬂuence of coastal environment factors on phytoplankton in Bohai Bay. The SEM is a multivariate statistical method and by using it, a researcher can construct theoretical concepts, test their measurement reliability, hypothesize and evaluate of a network of relationships between variables. In our study, the hypothesized model considered the inﬂuence of the physical environment (temperature, salinity, and PH) and nitrogen (total dissolved inorganic nitrogen, total dissolved inorganic phosphate, and silicate) on total phytoplankton biomass. With the conclusions of this model, we find that nutrients have greater effect on phytoplankton biomass and there is a strong correlation between nutrients and physical environment. Additionally, salinity has greatest positive effect on phytoplankton, whereas total dissolved inorganic nitrogen has the greatest negative effect. Generally, the SEM gave plausible results and enabled the identiﬁcation of the role of the abiotic factors on the phytoplankton.