We studied the effects of different temperatures, light intensity, nitrogen (N) and phosphorus (P) on the absorption of dissolved inorganic carbon (DIC) and pH-improving rate of Sargassum vachellianum. The results showed that:1) Temperature and light intensity all had a significant effect on the DIC sequestration and pH-improving capability of S.vachellianum (P<0.05). S.vachellianum shows the highest DIC sequestration[82.14 μmol/(g·h)] and pH-improving capability[0.138/(g·h)] when cultured at 20℃ and at a light intensity of 60 μmol/(m²·s). When the environmental conditions are below or above this threshold, the DIC sequestration and pH-improving capability of S. vachellianum appeared different degree reduction. 2) N and P enrichment could dramatically increase the DIC sequestration and pH-improving capability of S.vachellianum (P <0.05). The HNP group had significantly higher DIC sequestration and pH-improving capability than that of LNP group (P<0.05), and the addition of N and P showed strong complementary effects on improving the DIC absorption and pH-improving rate of S.vachellianum. The results could provide theoretical basis for the bioremediation and acidification mitigation by S.vachellianum cultivation in coastal eutrophication waters.