The total energy and cohesive energy of typical binary compounds, namely, NiAl, SiC, GaAs, MgS and NaCl, are studied by using he linearized augmented plane-wave method. Special emphasis is put on the effects of the choice of muffin-tin radii of the two elements. Results show that, for closely packed alloy NiAl, the variation of MT radius yields little change to the total energy; and the atomic covalent radii could be used in setting the MT radii for covalent crystals such as SiC and GaAs; but the ionic radii are not appropriate for crystals with strong ionic bonds such as MgS and NaCl due to a large number of core electrons lost out of the mufin-tin spheres of cations. The calculated cohesive energies with proper choice of muffin-tin radii are in good agreement with experimental results.