Abstract: Oleaginous microalga with rich polyunsaturated fatty acids（PUFAs）is considered an optimal raw material for the production of high-valued microalgae oil. The key screening indexes of high-valued microalgae include oil yield,neutral lipid fractionation,and PUFAs distribution. Low-nitrogen stress is one of the most effective approaches in inducing oil accumulation in microalgae. The changes in growth,lipid composition,and PUFAs distribution of Chlorococcum sp. were determined under 17.6 mmol/L NaNO₃,5.9 mmol/L NaNO_3,and 3.5 mmol/L NaNO₃. The results showed the total lipid yield reached 2.55 g/L and 2.51 g/L at 3.5 mmol/L and 5.9 mmol/L NaNO₃ group,respectively,much higher than that 1.43 g/L at 17.6 mmol/L NaNO₃ group. Lowering nitrogen concentration increased the proportion of neutral lipids,i.e.,it was the highest at 3.5 mmol/L NaNO_3,accounted for 88.6% in total lipid,higher than 86.3% at 5.9 mmol/L NaNO_3,and 80.5% at 17.6 mmol/L NaNO₃. Decreasing nitrogen concentration also changed the fatty acids distribution in different lipid fractionations and promoted the fatty acids more distributed in neutral lipids. For instance,at 3.5 mmol/L NaNO_3,the proportion of α-linolenic acid in neutral lipids increased to 86.5% at the end of the cultivation from 33.9% at the beginning of cultivation. Conclusively,appropriate nitrogen concentration has a great role in the improvement of total oil yield,neutral lipid fractionation,and PUFAs distribution;moreover,the accumulated C18：3（ω-3）in Chlorococcum sp. tends to be distributed in neutral lipids under low nitrogen,and thus Chlorococcum sp. is a potential oleaginous microalgae for the production of high-valued microalgae oil.

Key words: oleaginous Chlorococcum sp., microalgae oil, nitrogen concentration, lipid composition, fatty acids distribution