Abstract: The distribution of technetium in the co-decontamination tank (1A tank) of PUREX process was analyzed. The trend of technetium was determined by the co-extraction of Zr-Tc in the section of extraction, which is related with the distribution of nitric acid. The concentration of nitric acid shows significant influence on the co-extraction of technetium and zirconium. At c(HNO₃)<3 mol/L, the concentration increase of nitric acid prevents the hydrolysis of Zr⁴⁺ to promote the co-extraction of Zr-Tc. At c(HNO₃)≥3 mol/L, nitric acid is co-extracted with Zr-Tc. At the range of 0.5-5 mol/L, the nitric acid is in favor of the extraction of technetium. The higher nitric acid concentration makes more technetium to be extracted into organic stream in PUREX process.