The invention discloses an adjustable centering test clamp for the axial fatigue of a material, and a test loading determination method thereof. Traditional test devices and clamps for the axial fatigue of materials cannot ensure the high centering property of a test piece during test, so the accuracy of fatigue test data is affected. The clamp can eliminate misalignment caused by a test device byadjusting the position of a middle adjustment block in order to make the stress state of the test piece in a second force bar state, so the test piece is only subjected to pure axial load during thetest, and the high accuracy of the fatigue test data is ensured. The axial load is respectively applied to the test piece and an accompanying test piece through an upper pressing block and a lower pressing block by adopting load distribution loading, and the accurate distribution of the load is realized by changing a distance from each of the test piece and the accompanying test piece to the center of the clamp. The clamp and the method have the following greatest advantages: the influences of the misalignment of the traditional clamps and test devices on the axial load fatigue test data of the material can be avoided, and the accuracy of the axial load fatigue test data is greatly improved.