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In this paper, the preparation of rutile TiO₂ powder from titanium slag by microwave-assisted activation roasting followed by hydrochloric acid leaching was investigated. The effects of the additive Na₂CO₃ on the crystal form, cell, crystallinity, phase transformation, surface functional groups and micro-surface structure of the calcined product were systematically studied using X-ray powder diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The results confirmed that the strongest characteristic Raman bands of rutile TiO₂ and the weakest FT-IR bands of (CO₃)⁻² were found when the Na₂CO₃ mass ratio was 0.4. Accordingly, the crystallinity for the product, namely short rod structure rutile TiO₂ powder, reached its peak value of 99.21% with a corresponding average grain size of 43.5 nm. The excessive Na₂CO₃ was found to be disadvantageous for the crystallinity of the product, since it formed a coverage on the surface of titanium slag which prevented the oxidation reaction for the decomposition of anosovite.