309S austenitic stainless steel is one of the candidate materials for the canisters to store high-level waste. However, the corrosion resistance of 309S austenitic stainless steel makes it difficult to meet a design life of 100 years in the groundwater environment containing a Cl-. The corrosion resistance of 309S austenitic stainless steel was improved by adding N and Nb, and the differences in microstructure and corrosion resistance of experiment steel with different N and Nb contents were compared and analyzed. The microstructure and passivation film composition of the stainless steel were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Shape Measurement Laser Microscopy System (SMLMS) and X-ray photoelectron spectroscopy (XPS). The effect of N and Nb on material corrosion resistance was discussed. Electrochemical tests were carried out at the Gamy-Reference 3 000 workstation. A three-electrode system was used as an electrolytic cell. The potentiodynamic polarization curve of the sample was measured by the potentiodynamic method. After the open circuit potential stabilized, the test was performed at a scanning rate of 0.33 mV/s and a test interval of -1.0 to 1.5 V (vs.SCE). The impedance spectrum of the sample was measured by the potentiostatic method. The amplitude was 10 mV, and the test interval was 0.01~100 kHz. ZView fitted the impedance spectrum. The polarization curve results showed that the pitting electricity of 2# and 4# samples increased from 0.20 V of the original 1# sample to 0.50 V and 0.96 V after addition of N and Nb. The impedance spectra showed that the arc of capacitive reactance increased obviously after N and Nb were added. Corrosion loss tests were performed according to ASTM standard G31-72. The sample was cut into 24 mm × 18 mm × 3 mm, and then soaked in a container containing 6wt.% FeCl3-0.16wt.% HCl solution at 35 ℃ for 120 h. During the 120 h soaking period, after sampling, ultrasonic cleaning with 20vol.% HNO3 for 60 min was performed to remove the corrosion products. The surface roughness of 3# stainless steel increased to 4.43 times after corrosion, and the maximum depth of the pitting pit increased by a factor of 1.59. After addition of N and Nb, the maximum width and depth of the pitting pit decreased to 41% and 2%, respectively. The XPS results showed that Nb2O5 passivation film was formed, and Nb(C, N) was precipitated to inhibit the initiation and growth of pitting pits in 309S austenitic stainless steels. N may be involved in forming Nb2O5, which helps stabilize the passivation film. This finding is important for studying the effect of N on the composition of the passivation film. The partial conversion of N to NH4+ to increase the local pH value of the solution jointly improves the ability of stainless steels to resist Cl-, thereby improving the corrosion resistance of 309S austenitic stainless steel. It is proved that the combined addition of N and Nb significantly improves the corrosion resistance of 309S austenitic stainless steel.