The utility model relates to a steel bar tension test fixture at low temperature and ultra-low temperature environments and a test device thereof. The steel bar tension test fixture is clamped at the two ends of a steel bar to be tested and comprises a dowel bar and a self-locking connecting piece connected with the dowel bar; a self-locking chuck for clamping the steel bar to be tested is arranged inside the self-locking connecting piece; the self-locking chuck is fixedly connected with the steel bar to be tested through an anti-falling fixed ring; the anti-falling fixed ring is positioned on the outside of the self-locking chuck and is in threaded connection with the end, penetrating out of the self-locking chuck, of the steel bar to be tested. The bowel bar, the self-locking connecting piece, the self-locking chuck and the anti-falling fixed ring are utilized for clamping the steel bar to be tested, so that the purpose that the steel bar to be tested is completely arranged in a low temperature box is achieved, and uniform temperature distribution of the steel bar to be tested is ensured; moreover, a non-threaded portion of the steel bar to be tested is clamped through the self-locking chuck, so that the defect that the end of the steel bar is easy to break firstly in the testing process since the diameter of the end of the steel bar to be tested becomes smaller after thread machining is avoided, and the testing accuracy is ensured. The steel bar tension test fixture can be widely applied to steel bar tension tests at low temperature environment.