The invention relates to a preparation method and an application of a carbon nanotube-carbon-porous silicon composite material, and belongs to the technical field of biological waste resource integration. The method comprises the following steps: firstly, carrying out boiling treatment on a silicon-containing biomass acid to remove inorganic salt ion impurities, and filtering, cleaning, drying and grinding the product to obtain powder; adding the powder into an organic complex solution containing one or two of nickel and iron for normal-temperature impregnation; sintering the impregnated powder in an inert gas or vacuum to obtain carbon nanotube-carbon-porous silicon dioxide composite powder; adding magnesium powder for mixing or separate placement, and carrying out temperature rise reaction to obtain a magnesium thermoreduction product; boiling the obtained magnesium thermoreduction product by an acid, leaching the magnesium thermoreduction product by a hydrofluoric acid solution, and washing, filtering and drying to obtain the carbon nanotube-carbon-porous silicon composite material. According to the preparation method and the application of the carbon nanotube-carbon-porous silicon composite material, in-situ inheritance of a material composition and in-situ inheritance and improvement of a material structure are achieved; and the silicon/carbon composite material is uniform in shape, composition and distribution.