Abstract: The critical pitting temperature (CPT) of 316L stainless steel in Cl⁻ solution was measured by electrochemical potentiostatic polarization curve method. The results of electrochemical potentiostatic polarization curve method were calibrated by immersion method to determine the specific value of CPT. The accuracy of CPT was further verified by optical microscope. The results show that the CPT of 316L stainless steel base metal was 58 ℃ and 38 ℃ in the solution with Cl⁻ mass fraction of 0.01, 0.05 and 0.1, respectively. When the Cl⁻ mass fraction was greater than 0.1, the CPT was less than 22 ℃. After soaking the 316L stainless steel sample at this temperature for 24 h, it was found that the metastable rust spot had obvious pitting core.The solution temperature was reduced by 10 ℃, and then the sample was soaked. There was no obvious pitting core. The temperature could be used to determine the CPT of 316L stainless steel in the solution with Cl⁻ mass fraction of 0.01，0.05，0.1.