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According to the experimental results of the structural characteristics and the energetic state of the interfaces in the nanocrystalline (NC) materials that a reduction of grain size in nm regime would result in a decrease of interfacial excess volume and interfacial excess energy, a qualitative model explaining the abnormal Hall-Petch relationship in NC samples is presented. It can be deduced from this model that a thermal annealing to the as-prepared NC sample will relax the NC interfaces, and consequently increase the normal-abnormal H-P transition grain size, which is confirmed by the experimental observations in the literature. From this analysis one can see that the densification of grain boundary in the NC materials, which plays an important role in the mechanical behaviors, should be considered in any attempt to improve the properties of NC materials.