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Through the common-used acidic electroless nickel deposition system with hypophosphite, the electrochemical essence of catalytic activity of the substrate for electroless deposition was investigated. It is found that oxidation of hypophosphite is dominative for the electroless nickel deposition of the substrate by stable potential measurement, and there exists a typical reaction potential for the anodic oxidation of hypophosphite. On the basis of previously proposed oxidation model of hypophosphite, the necessary condition of the metal substrate with catalytic activity for electroless nickel deposition is put forward that the potential of the metal is not only higher than the redox potential of hypophosphite, but also lower than the metal’s potential of zero charge in the particular electrolyte. By examining the experimental results of five kinds of typical metal, the above hypothesis was proved.