Abstract: Multi-component determination of Sargassum horneri produced by the"golden tide"outbreak in the Jiangsu seas were performed to evaluate the quality and dominant component. And the antioxidant activity of different extracts of Sargassum horneri was studied for better utilization the reasouces to provide a reference. The conventional physical and chemical methods were used to compare and analyze the conventional nutrients and other active ingredients of Sargassum horneri with six other common brown algaes. The antioxidant activity of Sargassum horneri was preliminary determined through DPPH and ABTS free radical scavenging ability of different ethanol extracts. The results showed that there were significant differences in the contents of nutrients between Sargassum horneri and other brown algaes. Compared with other brown algaes, the quality of protein in Sargassum horneri was better and the protein amino acid composition conforms was close to the ideal protein amino acid composition model recommended by FAO/WTO. The fucoxanthin in Sargassum horneri was dominant component because the contents were significantly higher than that of other six brown algaes. Saturated fatty acids in Sargassum horneri was slightly higher than unsaturated fatty acids, relative content of palmitic acid, oleic acid and arachidonic acid were the highest in saturated fatty acids, monounsaturated fatty acids and polyunsaturated fatty acids, respectively. Sargassum horneri contained higher Zn and Fe among the 10 trace elements. According to the half clearance rate of free radicals (IC₅₀ value), the antioxidant capacity of each extract was evaluated. The antioxidant capacity order in DPPH system was:30% ethanol extract (IC₅₀=0.097 mg/mL) > 50% ethanol extract (IC₅₀=0.102 mg/mL) > 90% ethanol extract (IC₅₀=0.136 mg/mL) > water extract (IC₅₀=0.160 mg/mL) > 70% ethanol extract (IC₅₀=0.162 mg/mL).In the ABTS system, the antioxidant order was 30% ethanol extract (IC₅₀=0.028 mg/mL) > 50% ethanol extract (IC₅₀=0.033 mg/mL) > 70% ethanol extract (IC₅₀=0.044 mg/mL) > water extract (IC₅₀=0.055 mg/mL) > 90% ethanol extract (IC₅₀=0.066 mg/mL). It could be seen that 30% ethanol extract had better scavenging ability of DPPH free radical and ABTS free radical, and the highest correlation with soluble polysaccharide component was negative correlation. Therefore, the quality of a large number of Sargassum horneri resources produced by the "Golden Tide" disaster would have better protein quality, and it could be used as a source of fucoxanthin development, and 30% ethanol extract was the best as an antioxidant function product.