In this paper, Phaeodactylum tricornutum was used to study the compensatory growth of micro-algae under phosphorus limitation. Five P concentration levels were set up at 1/20(P₁), 1/10(P₂), 1/8(P₃), 1/4(P₄), 1/2 (P₅) of f/2 phosphorus media respectively, while f/2 culture media was served as control (Pck). P. tricornutum had been treated under phosphorus stress for 10 days, then, the nutrient stresses were removed by introducing f/2 media, the cultures were cultured for 16 more days with inoculative cell density (2.5×10⁵cells·mL^-1)and normal nutrients supply. Cell density, biomass, content of intracellular dissoluble carbohydrate and protein were measured during these two periods. It was found that cell density, biomass, content of intracellular carbohydrate and protein of P. tricornutum were lower than that of the control under phosphorus limitation (p<0.05). During the phosphorus recovery stage, cell density and biomass of P₁、P₂ and P₃ treatments were higher than those of the control during prophase and metaphase (p<0.05), and their maximal average relative growth rates were 0.73、0.70、0.68 d^-1 respectively, which were higher than that(0.55 d^-1) of the control(p<0.05). The difference of cell density and biomass between P₄ treatment and the control was not significant. The cell density and biomass of P₅ treatment were lower than control significantly during prophase and metaphase (p<0.05). As the culture time increased, the difference of cell density、biomass、content of intracellular protein and dissoluble carbohydrate between the treatments and the control trended to be equivalent.