The invention discloses a modified fly ash for reinforcing rubber products and a preparation method thereof. The modified fly ash for reinforcing rubber products provided by the invention comprises the following raw materials: fly ash, thermosetting resin solution and interface adhesive solution, wherein the weight ratio of the fly ash to thermosetting resin solution to interface adhesive solution is 100:(5-30):(5-20). A twice coating modifying method adopted for modifying the fly ash comprises the following steps: firstly, coating the thermosetting resin solution on the surface of the fly ash, and then coating the interface adhesive solution on the surface of the fly ash after the coating at the first time, thereby acquiring the modified fly ash. According to the preparation method provided by the invention, twice coating modification is adopted; the modification for the surface of the fly ash is uniform; an interface layer for strong-phase inter-acting force is formed between the fly ash and the rubber material; the bonding is more firm; the interfacial force transfer is uniform; the filling amount in the rubber products is increased; the mechanical property is increased; the preparation method provided by the invention has the advantages that the expensive coupling reagent and strong acid and alkali strong in corrosivity are not adopted, the cost is low and the operation is safe; a sealing pipeline is used for conveying the raw materials; the working environment is improved; the environmental pollution is reduced.