Accumulated annealing parameter has been widely used for indicating the corrosion resistance of Zircaloys. However, for Nb-containing zirconium alloys, a unanimous conclusion has not been drawn yet. Even more, some researchers confirm that the accumulated annealing parameter is totally inadequate in this type of alloy. Based on its physical nature, we summarize the correlation of the accumulated annealing parameter and alloy microstructure. Further, the reason why it can identify the corrosion resistance in some specific alloys is explained tentatively. It is suggested that the diffusion rate of alloying elements (Fe and Cr diffusing fast while Nb diffusing extraordinarily slow) determines whether the accumulated annealing parameter will work. A clear conclusion is drawn that the accumulated annealing parameter can identify the low-Nb zirconium alloy’s corrosion resistance, i.e., the smaller the value of the accumulated annealing parameter, the finer the second phase particles and then the better the corrosion resistance of alloy