The invention discloses an automobile inner decorative board made of composite materials of natural fibers / thermoplastic resin, and a mixing method of the composite materials of the natural fiber / the thermoplastic resin. The automobile inner decorative board is composed of at least a core layer and a surface layer. The surface layer is composed of the following main raw materials, by weight, 5-35 parts of spandex fibers, 25-45 parts of polyester fibers, 15-25 parts of low-melting-point and skin-core type composite fibers, and 15-35 parts of high-melting-point hot melting fibers, wherein the difference between the melting point of the high-melting-point hot melting fiber and the melting point of the low-melting-point and skin-core type composite fibers is larger than 20 DEG C. The core layer is composed of the following main raw materials, by weight, 5-35 parts of basalt fibers and / or glass fibers, 5-35 parts of the natural plant fibers with modified surfaces, 15-35 parts of polyester fibers, 15-25 parts of low-melting-point and skin-core type composite fibers, and 15-25 parts of high-melting-point fibers. The automobile inner decorative board and the mixing method achieve integration of manufacturing and forming of the composite materials, and the material manufacturing stage can assist the material forming stage directly and effectively.