Abstract: The difference between the national standard and American standard of charpy pendulum impact test has been investigated. Testing results indicate that the similar results can be obtained by the two methods when the impact absorbing energy is low. However, the impact properties obtained by ASTM E23-07a are higher than that of GB/T 229-2007 in case of high impact absorbing energy. This is mainly caused by difference in impact blade radius. A small plastic deformation will be occur when the contact area between impact blade and impact testing specimen is small, leading to a lower expansion and impact absorbing energy. Conversely, a big plastic deformation will be occur in case of big contact area between impact blade and impact testing specimen, causing a higher expansion and impact absorbing energy. The two methods of national standard and American standard have the same nominal size for specimen but quite different in machining deviation. Compared with national standard, the machining deviation requirement of American standard is stricter.