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Investigations are performed on low-temperature oxygen diffusion in the carbon vacancy ordered ZrC0.6 and thus induced formation of the oxygen atom ordered ZrC0.6O0.4. Theoretically, a superstructure of Zr2CO can be constructed via the complete substitution of carbon vacancies with O atoms in the Zr2C model. In the ordered ZrC0.6, the consecutive arrangement of vacancies forms the vacancy channels along some zone axes in the C sublattice. Through these vacancy channels, the thermally activated oxygen diffusion is significantly facilitated. The oxygen atoms diffuse directly into and occupy the vacancies, producing the ordered ZrC0.6O0.4. Relative to the ordered ZrC0.6, the Zr positions are finely tuned in the ordered ZrC0.6O0.4 because of the ionic Zr-O bonds. Because of this fine adjustment of Zr positions and the presence of oxygen atoms, the superstructural reflections are always observable in a selected area electron diffraction (SAED) pattern, despite the invisibility of superstructural reflections in ZrC0.6 along some special zone axes. Similar to the vacancies in ordered ZrC0.6, the ordering arrangement of O atoms in the ordered ZrC0.6O0.4 is in nanoscale length, thus forming the nano superstructural domains with irregular shapes. [ABSTRACT FROM AUTHOR]