By both test methods of rapid chloride migration（RCM） and coulomb electric flux, resistance of concrete of different mix proportion to chloride penetration after high temperature was measured. Results by two methods were compared with each other, and meanwhile concrete micro structure change before and after high temperature was also observed by SEM. Test results indicated both before and after high temperature, concrete strength has obvious effect on chloride penetration; with temperature elevated, chloride penetration is increased, which is extremely remarkable for 800℃; the main change trends of test results by both test methods of RCM and coulomb electric flux were similar, however, the former could more finely reflect the effect of high temperature on concrete pore structure; before and after high temperature, the concrete micro structure change is in accord with the degree of chloride penetration.