The angular distributions of sputtered Al and Sn atoms ejected from the Al-Sn multi phase alloy bombarded by 30keV Ar+ ion have been measured with collector technique and RBS analysis. The sputtered surface has been observed with scanning electron microscopy (SEM), and its compositions have been analyzed both in sputtered and unsputtered areas with electron x-ray probe microanalyser (EPMA). The results show that the angular distribution of sputtered Al atoms is nearly cosine, and that of Sn is over-cosine. To explain the experimental results we propose a reasonablt sputtering yield equation, Y(θ) = ∑Yi(θ) each , Yi(θ) stands for the sputtering yield of the area in which its surface topography and compositions is different from other areas.