Abstract: Under 1 keV Ar ion bombardment of Cu-Pt alloys at high fluence and low temperature, the depletion degree of the segregating species at the second surface layer, and the normalized sputtering yield ratios (non-segregating species/segregating species) in the near-normal direction (15°) and at oblique angle (75°), have been estimated by an improved kinetic BIGS (bombardment-induced Gibbsian segregation) model. For the bombarded Cu-Pt alloys, calculations show that the depletion degree of the segregating species at the second surface layer is small when its bulk composition equals the extreme value, but this depletion degree becomes large when its bulk composition equals the intermediate value. Furthermore, the difference of the normalized sputtering yield ratio between 15° and 75° is small when the buIk composition of the segregating species equals the extreme value, but this difference becomes large when that of the segregating species equals the intermediate value.