Due to nonuniform corrosion across the section of specimen, it is very difficult to obtain constitutive law of attacked concrete. A method combining experiment with simulation was proposed to solve the problem. Firstly, with Ficks second law, it modifies the mesoscope constitutive law of attacked mortar and interfacial transition zone(ITZ), with which the stressstrain curves of specimen exposed to sodium sulfate solution is simulated by using CT technique. Secondly, the strength reduction ratio of mortar and ITZ are identified with comparison of experiment results. Thirdly, with corrosion homogenization, the method simulates the constitutive law of uniformly attacked concrete. In view of the work above, it gives a procedure to analyze the constitutive law of attacked concrete in any location of concrete structure at any mass fraction of the attacker.