In the framework of Faber-Ziman’s formalism, the radial atomic number density distributions rho(r) for two amorphous ZrO2-gel samples have been derived, and used to perform local structure simulations based on the monoclinic and tetragonal crystal skeletons in order to determine and investigate the local structure of amorphous ZrO2. The results indicate that the topological structure of amorphous ZrO2 bears more resemblance to monoclinic ZrO2 structure than to the tetragonal one. Moreover, the random structure in the amorphous ZrO2 is characterized mainly by the first-kind disorder in the short-range. According to this structural picture of amorphous ZrO2, a phase-transition mechanism of amorphous ZrO2 has been proposed, by which the crystallization of amorphous ZrO2 is considered starting with the formation of monoclinic nuclei followed by their further growth or conversion to the tetragonal phase, depending on the particular kinetic conditions and chemical environments. This proposed mechanism can help in the understanding of some experimental results that are not yet well understood.