Abstract: The total chloride ion and free chloride ion contents of concrete were determined by natural diffusion method. Cl － binding capability was calculated for different kinds of concrete. The influences of the types of environmental media and chloride ion concentration on Cl － binding capacity were discussed. The results show that Cl － binding capacity of common concrete is weakened when composition of environmental medium becomes more complicated，concentration becomes higher and the number of ions is increased. The rule of mineral admixture concrete is basically the same. Cl － binding capacity of common concrete，fly ash concrete，silica fume concrete and slag concrete in ( 3. 5% NaCl + 5% MgSO4 ) solution are reduced by 38% ，36. 7% ，36% and 51. 7% separately， compared to the situation in 3. 5% NaCl solution，and those in Qinghai salt lake bittern are reduced respectively by 58% ，64. 7% ，74. 9% and 62. 1% ，from which it can be concluded that the weakening effect of concrete on Cl － should be taken into account in chloride salt environment under the situation of comparatively high concentration and complicated component.