The angular distributions and yields of silver atoms sputtered from a Ag sample have been measured using collector technique and RBS analysis. The Ag target was sputtered at normal incidence with 27keV Ar+ ions. The irradiated surface was examined by scanning electron microscopy. It was found that all the angular distributions were over-cosine with different irradiation dose, but the sputtering yields were dose-dependent. The experimental result can be explained with surface topography and sputtering yield as a fuction of the angle of incidence. It is found that surface topography seems to be an important factor to influence sputtering yield. a new concept, namely "apparent yield", is presented.