Abstract: In seaweed (Laminaria japonica) extraction processing, biological enzymolysis processing has been an ideal alternative to traditional chemical extraction method. In order to evaluate the extraction effects of three different processing methods, we treated the seaweed by chemical processing (CP), enzymolysis processing (EP) as well as combined enzymolysis and microbial fermentation processing (CEMP). Besides, we compared the contents of plant hormones and algiante oligosaccharides in addition to the molecular mass distribution in three kinds of seaweed extracts. We determined the alginate content, molecular mass of alginate oligosaccharide and plant hormones contents by m-hydroxydiphenyl method, HPLC and HPLC-MS, respectively. The results show that the CP method had the lowest extraction rate of alginate oligosaccharides (41.99%) with molecular mass of 200−400 D, while the EP method and CEMP method had relatively higher extraction rate of alginate oligosaccharides (90.75% and 82.21%) with molecular mass of 200−1 600 D. Indoleacetic acid (IAA) was the most abundant plant hormone among all the three extracts, ranging from 2.64 to 64.59 ng·g⁻¹, followed by jasmonic acid (JA, 0.05−13.09 ng·g⁻¹). The plant hormone content of the extract by CEMP method was higher than that of the other two extracts. Based on the comprehensive comparison of extraction rate of plant hormones and alginate oligosaccharides, the CEMP method is more suitable for the preparation of agricultural seaweed extract than the CP method and EP methods.