The conversion of free chloride ions into bound chloride ions in the concrete pore solution can effectively reduce the corrosion of reinforcing steel in reinforced concrete structures in coastal and salt lake areas.The effect of nano-calcium carbonate on chloride ions binding amount of cement stone was investigated. Potentiometric titration was used to determine the content of bound chloride ions, and the chloride ion binding capacity of cement stone was analyzed by plotting the fitted relationship curve between bound and free chloride ions according to chloride ion isothermal adsorption theory. The chloride ion binding mechanism of cement stone was analyzed by XRD and thermogravimetry analysis. The results show that the admixture of nano-calcium carbonate increases the chloride ion binding amount of cement stone, and the total bound chloride ions content is the largest when its admixture reaches 3% (mass fraction). With the increase of chloride ion concentration, the chloride ion binding amount of nano-calcium carbonate doped cement stone increases accordingly. The admixture of nano-calcium carbonate could accelerate the hydration of cement and promote the generation of C-S-H gel and Friedel’s salt, which is beneficial to the chloride ion physical adsorption and chemical binding of cement stone.