The invention provides a multi-layer filled composite flame-retardant thermal insulation board for a straw board, comprising an upper layer board, a lower layer board and a middle filling layer, wherein joints are connected by an inorganic binder, the filling layer comprises a plurality of grids, and the grids are internally provided with a plurality of layers of inorganic fiber insulation material. The grids are formed by intersected joint of side boards at the periphery and a plurality of partition boards. The upper layer board, the lower layer board, the side boards and the partition boardsare straw flame retardant boards. The multi-layer filled composite flame-retardant thermal insulation board made of flame-retardant crop straw boards adopts the crop straw flame-retardant boards as abasic structural skeleton material and is made into a multi-layer cavity structure, and a cavity formed by the straw boards is filled with the inorganic fiber insulation material to form the multi-layer filled thermal insulation board. Due to the flame retardancy of the straw board itself and the incombustibility of the filling material, the multi-layer filled composite thermal insulation board made by the patented technology has excellent fire safety.