The invention discloses an automatic preparation device for modified asphalt for a lab. The device comprises a tank body, an electric furnace plate, an upper cover and a telescoping rod, wherein the tank body is positioned on the electric furnace plate, and the upper cover is buckled to an opening in the top part of the tank body; a motor is arranged on the top part of the upper cover; the upper end of the telescoping rod is connected to an output shaft of the motor, and the lower end of the telescoping rod is inserted into the tank body; an stirring impeller is arranged at the lower end of the telescoping rod; a feeding port is formed in the side surface of the top part of the tank body; a discharging port is formed in the side surface of the bottom part of the tank body; a liquid level sensor for detecting the level of the asphalt in the tank body is arranged in the tank body; a temperature sensor for detecting the temperature of the asphalt in the tank body is arranged on the wall surface of the tank body; air exhausting holes are formed in the upper cover. With the adoption of the device, the asphalt stirring uniformity is ensured.