The growth condition of Skeletonema costatum was studied in different phosphorus concentration by the adding-nutrients experimental method and by batch culture experiments were conducted. PH, DOC, nutrients concentration of the culture medium and the N/P ratio of the cell were measured periodically. The results showed that the phosphorous concentration determined the growth rate of Skeletonema costatum and the maximum cell density. PH of the culture medium began to decreased drastically as soon as the exponential growth period was over. It seems to be a herald to the Skeletonema costatum growth condition. The DOC concentration increased faster in the culture medium with higher cell density as the result of the addition of more phosphate, and could still keep increasing trend for a while after the exponential growth period of Skeletonema costatum ended. The N: P ratio in the Skeletonema costarum cell was about 15:1. which was close to the Redfield ratio. From the N:P ratio in the cell, we could deduce that when the Skeletonema costatum enters a new environment, it first concentrates phosphorous, and then uses it later, the initial absorption rate of phosphorous was faster than that of nitrogen.