Abstract: In order to make full use of marine biomass resources,Laminaria japonica was used as raw material to extract sodium alginate by ultrasonic-complex enzymatic hydrolysis(including cellulase,pectinase and papain). Based on the single factor experiments of enzyme concentration,enzymolysis pH,enzymolysis temperature and ultrasonic power,the extraction process was optimized by orthogonal experiments. The results showed that the optimal extraction process was as follows:The cellulase concentration 0.3 g,the pectinase concentration 0.3 g,the papain concentration 0.1 g,enzymolysis pH=4,enzymolysis temperature 55 ℃,ultrasonic power 250 W. Under the optimum technological conditions,the yield of sodium alginate was 21.53%±0.12%,which was 1.288 times that of the traditional formaldehyde method. Through viscosity measurement,the viscosity of the obtained sodium alginate product was 1880 mPa·s.Through scanning electron microscope observation,it could be seen that ultrasonic-complex enzymatic hydrolysis could effectively destroy the structure of Laminaria japonica cell wall,thus improving the yield of sodium alginate. Ultrasonic-complex enzymatic hydrolysis could improve yield,reduce pollution and production cost,and had certain universality and broad application prospects.