Composite asphalt modifier applicable to modification of hard asphalt and preparation method of composite asphalt modifier

The invention relates to a composite asphalt modifier applicable to modification of hard asphalt and a preparation method of the composite asphalt modifier. The composite asphalt modifier comprises the following raw materials in parts by weight: 8-30 parts of natural rock asphalt, 10-30 parts of butadiene styrene rubber, 15-40 parts of a cosolvent, 2-10 parts of an asphalt modifier and 30-40 partsof polyphosphoric acid. The preparation method comprises the following steps: heating the polyphosphoric acid to 100-110 DEG C, keeping the temperature, heating SBS (Styrene Block Copolymers) and butadiene styrene rubber to 60-70 DEG C, further putting into the polyphosphoric acid at a temperature-kept state, heating to 110-130 DEG C, sequentially adding the cosolvent, the asphalt modifier, the natural rock asphalt and a nano material, and stirring for 5-30 minutes at a rotation speed of 100-200r/minutes, thereby obtaining the composite asphalt modifier. The composite asphalt modifier provided by the invention can be