To improve the thermal peeling resistance of Sn plating formed on a Cu-Ni-Si based alloy sheet containing Zn.

In the Cu-Ni-Si based copper alloy sheet containing, by mass, 1.0 to 4.0% Ni, 0.2 to 0.9% Si and 0.1 to 2.0% Zn, and the balance Cu with inevitable impurities, and subjected to solution treatment accompanied by recrystallization and aging treatment, metal Zn concentration upon sputtering by 0.2 m from the surface is controlled to 0.1 mass% by Auger electron spectroscopy. By using an N2-H2 gas as the atmospheric gas of the solution treatment or removing a surface layer by etching or polishing after the solution treatment, the metal Zn concentration can be controlled to 0.1 mass%.