Through the isothermal adsorption of chloride ion, the adsorption kinetics and the adsorption thermodynamics, the influence of polycarboxylate superplasticizer on the chloride binding in cement paste has been investigated. Besides, the influencing mechanism was examined by the X-ray powder diffractometer(XRD). It has been found that the polycarboxylate superplasticizer reduces the chloride binding, and the smaller the water-cement ratio is, the greater the effect is. Chloride binding onto cement paste with polycarboxylate superplasticizer in a short time conforms to pseudo-first-order kinetic equation, indicating the physical adsorption of chloride ions. In a long time, it conforms to pseudo-second-order kinetic equation, indicating the chemical adsorption of chloride ions. With the increase of content of polycarboxylate superplasticizer, the adsorption rate decreases. The free energy, enthalpy and entropy of chloride binding are decreased with the increase of polycarboxylate superplasticizer, and this process is spontaneous and exothermic. The influence of polycarboxylate superplasticizer on the chloride binding is mainly attributed to the physical adsorption, not chemical combination of chloride ions.