In this paper, $N{O}_2^{-}$ was intercalated into the interlayer of Zn-Al-LDHs (layered double hydroxides, LDHs) by hydrothermal method to prepare modified hydrotalcite (LDHs-NO₂), and LDHs-NO₂ was characterized. The effect of different LDHs-NO₂ content on the fluidity, mechanical properties, chloride ion diffusion coefficient, pore structure, chloride ion adsorption of cement mortar and corrosion resistance of steel bar was investigated. The test results show that the compressive strength and flexural strength of cement mortar are improved, and the chloride ion diffusion coefficient and porosity are decreased by adding different content of LDHs-NO₂ into cement mortar. Compared with the reference group, the performance of cement mortar with 2% (mass fraction) LDHs-NO₂ is the most significant. Then, with the continuous increase of LDHs-NO₂ content (4%, 6%), the fluidity and mechanical properties of mortar decrease, but still higher than the reference group. The porosity of cement mortar has increased, but it is still lower than the reference group. LDHs-NO₂ achieves the adsorption of Cl^- through interlayer ion exchange, which is accompanied by the release of interlayer $N{O}_2^{-}$ during the adsorption of Cl^-. LDHs-NO₂ can effectively delay the corrosion of steel bars in cement mortar, and the more LDHs-NO₂ content in a certain range, the better the corrosion resistance of steel bars.