Abstract: The impact value, obtained from routine impact test is one of the five most important mechanical properties, but it is still lack of definite physical meaning. By lusing a modern advanced impact testing machine in which the load-deflection curve can be measured, and the work for elastic deformation, plastic deformation, crack initiation and crack propagation can be differentiated. Fom this the stress-strain relationship during impact loading can be determined, and the relationship between fracture and impact pioperties can be established also. Therefoie, a method foi characterizing the fractme toughness of materials under impact loading was found.