The invention relates to a preparation method of a direct-stirring type SBS (styrene-butadiene-styrene) asphalt modifier and a preparation method of an asphalt mixture. The preparation method comprises the following steps of respectively metering 4303 star-shaped SBS, 1301 linear SBS and lubricating oil, feeding into a mixer according to a ratio, uniformly mixing, and uniformly stirring; feeding petroleum resin and calcium carbonate into the mixer, and uniformly stirring; feeding the mixture into a double-screw extruder, enabling the mixture to form a melting mixture at high temperature, and enabling the double-screw extruder to extrude the melting mixture after the forced shearing, extrusion, dispersing and kneading are continuously maintained; cooling the melting mixture extruded by thedouble-screw extruder by a water tank, enabling a pelletizer to cut into granules, enabling an air dryer to dry, and packaging. The preparation method has the advantages that the production technologyof the modified asphalt is simplified, the production quality of the mixture is favorably controlled, the construction quality of a road pavement is ensured, the use property of the road is improved,the service life of the road is prolonged, the pollution to the environment is decreased, and the engineering investment is reduced.