Many researchers have pointed out that the blended concrete which pfa, gbs or sf were added in have high ability of anti-chloride penetration. RCPT (Rapid Chloride Penetration Test, checking the columbus or conductivity of concrete samples) had been firstly used in Portland concrete, some doubts, however, have been expressed with regard to this test when used in blended concrete . The present article analysis the reason of the deviation caused by the supplementary cementing materials. At the same time, the author utilizes a method to correct the RCPT deviation used in blended concrete.Some researchers have claimed that the chloride difrusivity is not a constant, so it is not suitable to use it calculating concrete service life. In the present article, corrected conductivity method was hired to check the changes of the corrected relative chloride difrusivity.Some conclusions:Pore structure and pore solution influence the columns or conductivity, but pore solution has little effect on the chloride penetration. According to the phenomena of the adsorption by the solid and double layer electric theory, the pore solutions in the concrete can be divided into conductive pore solution, semi-conductive pore solution, and none conductive pore solution, the pore can be divided into conductive pore, semi-conductive pore and none conductive pore. Pore solution change is the main cause to make the rapid method cannot correctly reflect the real permeability of the blended concrete. The corrected results have better linear relationship with the 150-day salt ponding test and the ponding-toasting test and the conclusions were analyzed. The corrected relative chloride difrusivity of different blended concrete changes with time were analyzed by mathematic method, the best fitted equation is:The variety of the supplementary cementing materials decided n. The correctedrelative chloride diffiisivities of blended concrete have more apparently changes with time. The new chloride difiusivity model isThe constant of n can be obtained by and the diffusivity model.