The invention discloses a device and a method for monitoring the internal settlement deformation of a high-filled roadbed on the top of a culvert. The device comprises a flat plate, a first pipe fitting, a second pipe fitting, a first measuring rope, a second measuring rope, expansion bolts and balancing weights which are arranged in a culvert or a fill stratum above the culvert. The flat plate islocated in the fill stratum above the culvert and fixedly connected with the first pipe fitting and the first measuring rope. The top end of the first pipe fitting is connected to the center of the flat plate, the bottom end of the first pipe fitting is connected or communicated with the second pipe fitting, and the first pipe fitting is a telescopic pipe fitting. The second pipe fitting comprises a plurality of sections which are connected, the first measuring rope passes through the first pipe fitting and the second pipe fitting, and the bottom end of the first measuring rope is connected with one balancing weight. The top end of the second measuring rope is connected with the expansion bolt inserted into the top structure of the culvert, and the bottom end of the second measuring ropeis connected with the other balancing weight. According to the invention, the deformation of any structure and most of the fill stratum in the roadbed can be measured.