The invention relates to a composite inclined-type coal-burning device for a boiler. The composite inclined-type coal-burning device comprises a coal hopper, a boiler body, a boiler arch, a fire grate and an ash pit, wherein the coal hopper is arranged at an inlet of the boiler body; a boiler top is arranged at the top of the boiler body; the ash pit is arranged at the bottom of the boiler body; the boiler arch and the fire grate are arranged in the boiler body; the fire grate consists of a frame and a plurality of fire grate segments; the side surface of each fire grate segment is rhombic; and the fire grate segments form a horizontal and inclined step-type rectangular fire grate surface. The composite inclined-type coal-burning device for the boiler is scientific in design, reasonable in structure, simple and convenient to use and high in practicability, and has the advantages of small size, good burning effect, low manufacturing cost, little air pollution, etc.