The invention relates to a combined inducer inducing marine microbial fermentation to produce K-carrageenase, and belongs to the technical field of microbial fermentation. The combined inducer comprises the following constituents by weight: 0.5 to 1.5 parts of fructo-oligosaccharide, 1 to 3 parts of K-carrageenan, and 0.5 to 1.5 parts of yeast extract. Fructo-oligosaccharide, K-carrageenan and yeast extract are mixed according to a certain proportion to serve as the enzyme production inducer, of marine microorganisms, used for fermentation in K-carrageenase production. Via 48 hours' flask shaking for oscillation fermentation, the K-carrageenase activity of Thalassospirasp. Fjfst-332 is 351 U/mL, and compared with the enzyme activity 54.3 U/mL of K-carrageenase of abacterial strain not added with the inducer, the enzyme activity is improved by 6.46 times.