Abstract: An experimental research is made on the involving physical short fatigue crack propagation of 1Cr18Ni9Ti pipe-weld metal with a replicating technique. Based on the "effective short fatigue crack criterion"（Fatigue Fract. Eng. Mater. Struct., 1999, 22（6）: 459-468）, the result revealed that the propagation of dominant effective short fatigue crack （DESFC） and the propagation of effective short fatigue cracks （ESFCs）, and their coalescence between ESFCs and DESFC contribute directly to the fatigue damage of material. The non-ESFCs in a form of the densities of ESFCs located ahead of the two tips of the DESFC contribute indirectly to the fatigue damage. In this physical short crack （PSC） regime, it exhibits a weakening micro-structural affecting with respect to a decrease of the densities of ESFCs, and thus the DESFC acts gradually as a long crack. Correspondingly, an agreement of involving statistical behaviour between the densities of ESFCs and the DESFC growth rates is observed. Thus, it is indicated that the difference of the involving micro-structural conditions for the DESFC initiation and growth between the sampling specimens is the intrinsic cause of the involving random fatigue properties. And the fatigue damage process is gradually from a initial chaotic state, to an independent random state at the transition of the micro-structural short crack regime and PSC, and then, to a historic dependent random state in PSC regime of fatigue damage.