Abstract: Influence of loading sequence on critical fatigue damage parameter D_c of 10CrNiMo steel was investigated in the loading sequence from high to low and reversedly, adopting six-piece smooth specimens for each sequence under cantilever bend loading.The test values were evaluated by type A standard uncertainty.The results manifested that as the loading is in a sequence from high to low, D_c ranges from 0.74 to 0.84, less than 1 and relatively stable, while as the loading is in a sequence from low to high, D_c ranges from 1.06 to 1.27, more than 1 with a little fluctuation.The average of different D_c from the two types of loading sequence was nearly 1.Type A standard uncertainty of D_c corresponding two types of loading sequence was 1.5% and 3.2% respectively.