Abstract: Uniaxial high-speed tensile tests were carried out on cast iron and cast aluminum round bar samples at different strain rates, their dynamic mechanical behaviors and broken conditions were studied, and the effects of related factors on tensile test were analyzed. The results show that methods of strain and stress testing, gauge length and clamping end length of samples had great influence on accuracy of tensile test and the oscillation degree of curves. Using fixtures with high specific stiffness and strength, and samples with short gauge length, testing stress with strain gauge, testing strain with two cameras and increasing the clamping end length appropriately could improve the accuracy of test results.