The invention belongs to the technical field of polyurethane sponge. The invention discloses a preparation method of polyether-type polyurethane sponge with a flame-retardant function. The preparation method comprises the steps of preparing materials, mixing the materials, stirring, feeding, foaming, carrying out the after-treatment and the like, and in the material preparation process, raw materials such as first polyether polyalcohol, second polyether polyalcohol, third polyether polyalcohol, butyl rubber, a first catalyst, a second catalyst, silicone oil, water, a foaming agent, MDI isocyanate, flame-retardant additive, chain extender and the like. The preparation method of the slow-resilience polyether-type polyurethane sponge is simple in process, high in production efficiency, capable of being produced by utilizing the existing equipment, and capable of being rapidly put into production; and the slow-resilience polyether-type polyurethane sponge prepared by virtue of the preparation method in the invention has good slow resilience and excellent flame retardant property.