The functionally graded interface (FGI) effects of a laser-discretely treated steel substrate and Cr electroplate are investigated in order to reveal the mechanism that the service life of the chromium-coated gun tubes is increased by laser-discretely pre-treating. The results show that a periodically graded structure is created on the surface layer of steel substrates due to laser-discretely pre-treating, and the periodically graded microstructural characteristics are inherited by the initially deposited chromium layer. Thus, there is an FGI layer between steel substrates and Cr coatings. The FGI layer can decrease the hardness gradient, and largely improve the corrosive-spallation resistance of Cr electrodeposits.