Abstract: In order to alleviate the toxic effects of offshore oil spill stress on Marine microalgae, adding different carbon sources may be one of the effective ways. By adding different concentrations of glucose (C₆H₁₂O₆) and sodium bicarbonate (NaHCO₃), the alleviation effect of exogenous carbon sources on the toxicity of Nitzschia closterium under 180# fuel oil dispersion (WAF) stress was investigated. Under different concentrations of NaHCO₃, the cell density and Chl a content increased, while the level of lipid peroxidation decreased. Four days later, the fatty acid composition of N. closterium was basically the same as that of the normal group, and the toxic effect was obviously relieved. Different concentrations of C₆H₁₂O₆ reduced the content of Chl a in N. closterium and increased its C18:1n-9 ratio significantly. Low concentration of C₆H₁₂O₆ had less alleviation effect on the toxic effect of N. closterium under WAF stress, while high concentration of C₆H₁₂O₆ aggravated the toxic effect of WAF, resulting in more serious lipid peroxidation. Therefore, adding an appropriate concentration of NaHCO₃ could alleviate the toxic effect of WAF on N. closterium to a certain extent.