The invention discloses a preparation method of silicon-iron composite aerogel, and particularly relates to a preparation method of silicon-iron composite aerogel. The silicon-iron composite aerogel is prepared from silicon dioxide-iron oxide aerogel and silicon dioxide-iron aerogel. The preparation method is characterized by comprising the following steps of using acid silica sol as a raw material, using an aqueous solution of sodium hydroxide or sodium carbonate, sodium hydrogen carbonate and ammonia as a gel catalyst, using an iron salt as an iron source and a gel accelerant, gelling in a water phase, afterwards, carrying out solvent replacement by using ethanol, and meanwhile, aging; completing modification by using a hexamethyldisiloxane solution of hexamethyldisilazane as a modifyingagent, so as to subsequently obtain a SiO2-Fe2O3 aerogel block, further, reducing by using hydrogen, so that SiO2-Fe2O3 aerogel can be made. According to the preparation method, an inorganic siliconsource-the acid silica sol which is low in price is used as a raw material; the production cost is lower and the prepared aerogel is better in performance.