One-part alkali-activated nickel slag cement was prepared by mechanochemical method. The carbonation resistance of one-part alkali-activated nickel slag cement mortar prepared with different alkali activators were tested， to study the effect of CO₂ volume fraction on the carbonation resistance of one-part alkali-activated nickel slag cement mortar. The mechanism was analyzed by pore structure analysis and X-ray diffraction（XRD） analysis. The results show that the carbonation products of the cement mortar are not related to the type of alkali activator， but to the CO₂ volume fraction. The carbonation products of the cement mortar tested at 3% CO₂ volume fraction are carbonation products， and the carbonation rate is much lower than that at 10% and 20% CO₂ volume fractions. The carbonation products of the cement mortar tested at 10% and 20% CO₂ volume fractions are carbonate and bicarbonate products. The carbonate is better than bicarbonate in pore filling， so the pore structure and compressive strength of the mortar after carbonation at 3% CO₂ volume fraction is better than those at 10% and 20% CO₂ volume fractions.