In order to investigate the effect of triacontanol on growth of Sargassum horneri, different concentration of triacontanol applied continuously for 20 days, or the thalli were immersed in triacontanol solution at concentration of 0.1, 0.5, 1.0 and 2.0 mg/L) for 24 h and then cultured in normal conditions for 20 days, and then the relative growth rate (RGR), physiological and biochemical indexes (photosynthetic pigment, soluble protein, soluble sugar) and fucoxanthin contents were determined, respectively. The results showed that after continuous application of 5 days, the RGR, chlorophyll a (Chl-a), carotenoid (Car), soluble protein, soluble sugar contents were significantly higher than the control; on the 15^th day, the growth of the 2.0 mg/L group was inhibited, and all the physiological indexes decreased significantly; on the 20^th day, the growth of the 0.1 mg/L group was still promoted, the other three higher concentration groups were inhibited by different degrees, and the higher concentration of triacontanol, the more obvious inhibitory effect. The immersed group after 5 days of culture, the RGR, Chl-a, Car, soluble protein and soluble sugar contents increased significantly; on the 10^th day, the RGR of 0.5 and 1.0 mg/L groups were significantly higher than the control; on the 15^th day, there was no significant difference with the control, and considering the physiological and biochemical indexes, 1.0 mg/L group was the most obvious effective group, and the promotion effect could maintain about 10 days after treatment. Fucoxanthin contents were significantly higher than control in treatment groups except continuous application with 2.0 mg/L triacontanol for 20 days, among which the fucoxanthin content increased 79.5% on the 10^th day after immersed treatment in 1.0 mg/L triacontanol solution for 24 h. Therefore, continuous application of low concentration of triacontanol (0.1 mg/L) or immersed in 1.0 mg/L triacontanol solution for 24 h every 10 days could significantly promote the growth and accumulation of fucoxanthin of S. horneri.