Abstract: Based on the damage mechanics theory, a new testing method in measurement of fatigue damage of metallic materials was proposed. The relation of fatigue damage of metallic materials such as 10CrNiMo steel to one of its macro-parameters displacement characteristic at loaded point was investigated under cantilever bend loading and adopting smooth plate specimens.The results manifested that fatigue damage of metallic materials and its displacement characteristic peak value at loaded point satisfy a special functional relation, through which fatigue damage of metallic materials could be measured indirectly by inspecting change of displacement characteristic peak value. The measured fatigue damage value could be compared to critical fatigue damage value and could provide reference for safe service and remaining life evaluation of metallic materials.