A double brake structure includes a line reel rotatably provided, at least one set of centrifugal pin, a centrifugal brake ring movably provided in the centrifugal brake ring, a centrifugal assembly for making the centrifugal pin be close to an inner wall of the centrifugal brake ring and making the centrifugal pin rotate in the centrifugal brake ring when the line reel is rotating, and for automatically adjusting the kinetic friction force between the centrifugal pin and the inner wall of the centrifugal brake ring according to the speed of the line reel when the centrifugal pin contacts with the inner wall of the centrifugal brake ring, and a magnetic brake mechanism for adjusting the speed of the line reel. The present disclosure is easy to use with stable brake performance, and can achieve the function of automatic compensatory braking.