Abstract: In natural waters, the growth of phytop lankton was mainly affected by nitrogen, phosphorus and N:P ratios. In this paper, three rep resentative HAB algae isolated from the coastalwaters of China, Prorocentrum donghaiense, Phaeocystis globosa and Pseudonitzschia pungenswere chosen for the research. Effects of different N:P ratios on the growth of these algae were tested in laboratory. This culture was grown in f/2 media at ca124℃ with salinity of ca130, light intensity of ca1.20μE/m2 ·s, and light2dark cycle of 12:12. Nitrogen and phosphorous starved cells of the species were obtained bygrowing the cells in f/2 media without addition of nitrogen and phosphorous until the ambient nitrogen or phosphorous had been dep leted for 3 days1Such cellswere used to test differentN:P ratios on the growth rate of three HAB algae under twoconditions of low-phosphorus (01362μmol/L PO3-42P) and high phosphorus (3612μmol/L PO3-42P), the N:P ratios of 0, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 50:1 and 100:1 were adop ted, respectively1The results showed that the op timum N:P ratios of P1donghaiense, P1 globosa and P1 pungens were 30:1, 30:1 and 10:1 respectively. While N:P ratios below 100:1, the relevancy between growth rate of the algae and nutrients concentration was more significant than that between growth rate and N:P ratios.P1 donghaiense and P1 globosa required high concentrations of nutrients, and growth rates inlow phosphorus conditions were much less than that in high phosphoruswaters; compared with two algae above mentioned, P1 pungens demanded less nutrients, and maintained high growth rate under low phosphorus conditions.