The catalytic system Sc³⁺-NH₄Cl-Cupferron (Cup)-diphenylguanidime (DPG) suggested by Yao et al gives a sensitive derivative wave in single sweep polarograph.The linear relationship between the wave bights H_w and the concentration of SC³⁺ in the range of 10^-7～10^-6 M has been used successfully in the ores analysis for Sc, We compared the waves in single sweep polarograph with that in the do polarograph and applied several electrochemical methods to investigate the mechanism of this wave, The experiments of electrocapillary curves, variation of the height of the mercury column and the time of the rest period befere scanning, the temperature coetlicent, cyclic voltammetry etc, indicated that the wave is adsorptive complex in nature and the ligand-Cupferron in the complex is catalytically reduced but not the canon Sc³⁺ therefore we call such catalytic wave as "adsorptive-complex wave".