The invention discloses a device and a method for testing thermal storage stability of modified asphalt. The device comprises an upright post, a platform, a first sample ring, a second sample ring, a sample cylinder, a first cross brace, a second cross brace, a top cover and a base, wherein the upright post is vertically fixed on the platform, the base is located on the platform, the first sample ring and the second sample ring respectively sleeve the upper and the lower ends of the sample cylinder, the top cover is located at an opening in the top of the first sample ring, and the lower end of the second sample ring sleeves the base; one end of the first cross brace is fixed at the joint between the first sample ring and the sample cylinder, one end of the second cross brace is fixed at the joint between the second sample ring and the sample cylinder, the other ends of the first cross brace and the second cross brace are connected with the upright post, and the first sample ring, the second sample ring and the sample cylinder are vertically distributed. The device is relatively high in measurement accuracy and testing efficiency, simple in structure, convenient to operate and relatively low in cost and can be repeatedly used.