The invention discloses a gene sequence of endo alginate lyase and application of the endo alginate lyase. The invention further discloses a technical method using genetic engineering. A gene of novelalginate lyase is cloned to an expression vector of escherichia coli, a recombinant escherichia coli strain capable of expressing the alginate lyase heterologously is obtained, the heterologous expression of the alginate lyase FsAlgB is achieved by the strain, and the function that sodium alginate is degraded to prepare sodium alginate oligosaccharide is achieved. The provided alginate lyase AlgLcan be widely applied to the fields of chemical industry, agriculture, food, feed addition, medicine, seaweed genetic engineering and the like.