Abstract: The fatigue crack propagation rate with probability (P) for welded by joints of ADB610 steel were investigated through fatigue crack propagation experiments. The joints were welded using shielded metal arc welding method. Twice seven data fitting method was adopted to calculate fatigue crack propagation rate of each sample in a series of same crack length. And it was calculated for the standard deviation of logarithmic fatigue crack propagation rate, and fatigue crack propagation rate with P=50%, P=90%, P=95%, P=99%, P=99.9% of base material(BM), heat affected zone (HAZ) and welded material (WM). The results show that the dispersibility of fatigue crack propagation in BM is the least, and the one in WM is the maximum. And when the probability is in the same, the speed of crack propagation in BM is the quickest and the one in WM is the slowest during the early stage of fatigue crack propagation, but during the last stage of fatigue crack propagation the difference of crack propagation speed in BM, HAZ and WM is not significant. And with the probability increase, it is decreased for the crack length corresponding to the insignificant difference for the three zones.