Abstract: Under the same sampling direction, geometrical dimension, machining method and machining precision, the fatigue crack propagation test was carried out on 20 mm thick ADB610 steel plates with different loading modes, loads and stress ratios. The fatigue crack propagation length a and cyclic life N or the a-N test data of ADB610 steel under different conditions were obtained. The a-N test data were combined with the K addition method and the K drop method for experimental analysis. The results show that when the initial maximum loads are the same, the initial starting positions of the two lg (da/dN) -lg (ΔK) are the same; When the initial maximum loads are different, the starting positions are different.