Abstract: Vickers-hardness test is widely used in metallic material performance test. The relationship between different test loads and the maximum probable relative errors or measurement uncertainty was discussed by mathematical simulation. The results show that with the increase of test load the maximum probable relative error and its uncertainty decreased at the magnification of 400 times. Whenever possible, larger test loads should be chosen to improve the test accuracy and repeatability. In the actual testing process, micro Vickers-hardness had better not be chosen.