Some Portland cement pastes with different contents of fly ash（FA） and ground granulated blast furnace slag（GGBS） were immersed in NaCl solution with different concentrations for corrosion experiments. Through silver nitrate titration， X-ray diffraction（XRD） and thermodynamic simulation， the variation rule of free chloride concentration in solution and the contents of various phases in cement pastes were analyzed. Results show that addition of FA and GGBS will reduce free chloride concentration in NaCl solution and improve the chloride binding capacity of hardened cement pastes. Addition of GGBS will result in an increase of AFm phase and an improvement of chemical binding capacity of chloride in hardened cement pastes. Meanwhile FA can improve the physical binding capacity of C-（A）-S-H in hardened cement pastes， the hardened cement paste with FA content of 40% has the optimum physical binding capacity of chloride.