An inclined layered solid-filling mining method in an ultrathick coal layer is applicable to exploitation in a “three-unders” ultrathick coal layer. In this method, the number of inclined layers is determined based on a principle of layered thickness from 2.5 m to 4.5 m, and a layered-exploitation downward-filling exploitation order is adopted. Tunnels and equipment are arranged according to a conventional solid-filling mining method. A cyclic order of mining, layout of metal meshes (14) and bamboo fences (24), and filling is adopted, so as to accomplish filling and exploitation of a first mining face and a first layer (21). Meanwhile, 4 months after the working face of this layer is finished, at a corresponding position in a second layer (22), under the cover of an artificial ceiling formed by the first layer (21), exploitation is performed by using the same filling mining method; such a cycle is repeated, and exploitation in a current layer is performed under the cover of an artificial ceiling fabricated by an upper layer, until the entire ultrathick coal layer is finished. When this method is adopted to exploit “three-unders” ultrathick coal layer resources, strata movement and earth surface subsidence may be effectively controlled; the method has a high extraction rate, high production efficiency, and low cost.