Abstract: Effects of nutrient elements, such as nitnogen, phosphor, silicon and iron, on growth and lipid accumulation of Phaeodactylum tricornutum were investigated by Nile-red fluorescence method. The results showed that higher nitrogen content would enhance the growth of algal cell and the optimal concentration is 1.76 mmol/L. Nitrogen deficiencies (0.22-0.44 mmol/L) induced the lipid synthesis remarkably. Phosphor deficiencies inhibited the growth of cells, but greatly induced the lipid synthesis. Silicon deficiencies caused a slow down on cell growth, but little effect on lipid accumulation. Either iron deficiency or iron excess (0.048 mmol/L) would enhance the lipid accumulation in P. tricornutum cells. In two-stage culture method, the first step is to grow cell in the nutrients-abundant medium and then transfer it to nitrogen/phosphor-deficienct medium for lipid induction in the second stage. The fat content of algal cell can be improved significantly by two-step culture method. Seawater is feasible to be used as a good lipid induction medium for P. tricornutum.