Ocean acidification is increasingly become one of research hotspots of marine science.Many scholars have investigated the effect of ocean acidification on phytoplankton populations.However,there still exist academic controversy on the influence of ocean acidification on the growth characteristics and response of phytoplankton populations because of the limitation and uncertainty of ocean acidification studies.We studied two of the typical diatom species,Phaeodactylum tricornutumand Chaetoceros curvisetus(harmful algae)to assess the effect of future CO_2-driven ocean acidification(the future level of the year 2100)on the growth of phytoplankton populations,aiming to predict the response of marine diatoms to future global climate change and provide data base to the research of elevated CO_2impact on marine organisms and biodiversity. CO_2enrichment experiments were carried out under specific CO_2concentrations.The control groups were bubbled with CO_2of 395muatm (ambient atmosphere level)and the experimental groups were 1,000muatm (future scenario of 2100year).Results showed that the environmental pH in experimental groups had reduced since the effect of CO_2-driven ocean acidification and the average pH level reduced approximately 0.3~0.4.The growth of P.tricornutumand C.curvisetus was promoted significantly by elevated CO_2concentration.The average specific growth rate(mu)of P.tricornutumgroups and C.curvisetus groups had increased by 33.1%and 13.4%,respectively,compared to their control groups.CO_2-driven ocean acidification can lead to the increase of dissolved inorganic carbon(DIC)concentration in the culture environment and relieve the limitation of inorganic carbon utilization during the growing period.Then,the growth can be promoted.Since diatoms account for a large part of marine primary productivity,the positive effect of ocean acidification on their growth may have ecological consequences in marine food chain in future.Additionally,elevated CO_2may lead to the break out of harmful algal blooms(such as C.curvisetus blooms)and be a threat to the stability of marine ecosystem and biodiversity.