Abstract: Skeletonema costatum, Hereosigam akashiwo and Alexandrium tamareme were used to investigate the impact of different nutritional conditions on growth under restricted CO₂ conditions.Biomass, pH and PO₄-P were measured to discuss how carbon source and different nutrition conditions effect the change of pH during the different growth phases.The results showed that the increase of pH in the carbon restrict system was higher than that in the no carbon restrict system.The pH of Skeletonema costatum in normal, nitrogen and phosphorus deficiencies increased by 1.4, 1.5 and 1.4, respectively.The pH of Hereosigam akashiwo increased by 1.2, 1.1 and 1.0, respectively.The pH of Alexandrium tamarense increased by 1.6, 1.6 and 1.8, respectively.The pH and biomass had a significant positive correlation; the pH and phosphate had a significant negative correlation.