The invention discloses a three-point or four-point bending fatigue test fixture for a living rat ulna. The fixture comprises a carrying disc and a foreleg uploading test device, wherein the carrying disc is arranged in a test chamber; the foreleg uploading test device comprises an upper connecting rod, an upper spring connection shaft, a linear elastic spring, a lower spring connection shaft, a T-shaped upper pressure head slide carriage, upper pressure heads, lower support heads, a C-shaped lower slide carriage and a lower connecting rod; the C-shaped lower slide carriage is mounted on the lower connecting rod connected with a main engine load sensor, and the upper end of the C-shaped lower slide carriage is provided with at least two guide pillars; a linear bearing capable of enabling the T-shaped upper pressure head slide carriage to move up and down along the guide pillars is mounted on the T-shaped upper pressure head slide carriage, the top of the T-shaped upper pressure head slide carriage is provided with the lower spring connection shaft connected with the lower end of the linear elastic spring, the upper end of the linear elastic spring is mounted on the lower end of the upper spring connection shaft, and the upper spring connection shaft is mounted at the lower end of the upper connecting rod; and one or more upper pressure heads are arranged under the T-shaped upper pressure head slide carriage, two lower support heads are arranged on the C-shaped lower slide carriage corresponding to the lower part of the upper pressure heads, and the carrying disc is mountedunder the lower support heads. The fixture provided by the invention can take a living rat as a carrier, and is simple in structure, convenient to use, precise in acting points, accurate in location and more excellent in microdamage research, thereby being suitable for performing the three-point or four-point bending fatigue test on the living rat ulna.