NOVELTY - Method for producing biogas by kelp residues through two-phase anaerobic fermentation involves (a) adding anaerobic fermented fresh activated sludge to kelp residues to obtain methane-producing strain, (b) adding anaerobic fermented activated sludge to kelp residues and solid waste discharged from fish breeding to obtain strain for acid hydrolysis, and (c) mixing kelp residues and cultured solid waste, inoculating the strain for acid hydrolysis, performing anaerobic fermentation, and adding the methane-producing strain, and performing anaerobic fermentation.    USE - The method is useful for producing biogas by kelp residues through two-phase anaerobic fermentation (claimed).    ADVANTAGE - The method enables to produce product simply, cost-effectively, and environmentally-friendly, and which enables to increase transformed utilization rate of the kelp residues, methane content, system stability, and yield, and solve resource utilization of the sea-cultured solid waste.    DETAILED DESCRIPTION - Method for producing biogas by kelp residues through two-phase anaerobic fermentation involves (a) adding 20% anaerobic fermented fresh activated sludge to kelp residues at 35 plus minus 1 with pH of 7-9 for 18-20 days to obtain methane-producing strain, (b) adding 30% anaerobic fermented fresh activated sludge to kelp residues and solid waste discharged from fish breeding, where the ratio of the kelp residue and solid waste discharged from fish breeding in a ratio of 4:2-3, performing culturing at 35 plus minus 1 degrees C with pH of 5-7 to obtain inoculating strain for acid hydrolysis, (c) mixing kelp residues and cultured solid waste in a ratio of 4:2.5-3.5, and inoculating the strain for acid hydrolysis, where the mass ratio of the acid hydrolysis strain and kelp residue is 1-3:10, (d) adding distilled water to the inoculated mixture, modulating the pH of the mixture, and performing anaerobic fermentation at 35 plus minus 1 degrees C for 72-96 hours, and (e) adding the methane-producing strain to the fermented liquid in a mass ratio of 1:5-9, and performing anaerobic fermentation at 35 plus minus 1 degrees C with pH of 7-9 to obtain finished product.