Abstract: Effects of the length-to-diameter (L/D) ratios of specimens on the experimental results were studied by using a split Hopkinson tensile bar, rotating disk indirect bar-bar tensile impact apparatus. The length-to-diameter ratios of the LY12 specimens used in the test range from 1 to 5. Results show that the specimens of L/D2.67 can be used to obtain exact parameters of materials under the proposed conditions, but the specimens of L/D2 can not be used in impact tensile test.