Abstract: In this work, the service environment of metal materials used in the evaporation and concentration process of the mother liquor after plutonium oxalate precipitation was simulated, and the corrosion behavior of 316L stainless steel plate and its welding samples in the mixed oxalic-nitric acid was studied according to the requirements of GB/T 4334.3-2000. The corrosion rates were obtained by weighting method, and the corrosion morphology of metal surface was observed by scanning electron microscope, and the distributions of surface elements before and after corrosion were analyzed by energy spectrum, and the concentrations of metal ions in the corrosion solutions were determined. The results show that the corrosion rates acquired by simulating corrosion tests are relatively low, and the corrosion is uniform. The average corrosion rates of 316L stainless steel plate in 8.0 mol/L nitric acid at 103 ℃ are 0.049 6 g/(m²·h) for plate and 0.068 6 g/(m²·h) for weld respectively. The research results provide data reference for the material selection of the equipment used in the evaporation and concentration process of the mother liquor after plutonium oxalate precipitation. The optimization of welding process is an important improvement direction for the use of 316L stainless steel as this equipment.