Abstract: The color reaction condition of KI and Pd(Ⅱ) is studied, which shows that in the pH=2 medium of hydrochloric acid, the mixture of Pd and excesive KI will become the orange-red. The apparent molar absorptivity, ε is 1.06×10~⁴ L· (mol·cm)^-1 at 408 nm, the maximum absorption wave length Palladium obeys beer's law in the range of 0-7.2 μg / mL. The recovery is 100.5%, the relative standard deviation is < 2.0 %. The limit of detection is 0.011 μg/mL. In comparsion with Inductively Coupled high-frequency Plasma-atomic Emission Spectrometry (ICP-AES), with this method shows no obvious discrepancy from it, which can be used to determine the Palladium in the soak solution of catalyst simply, quickly, and sensitively. The results have proved to be satisfactory.