Structural, electronic properties of the SnxIn(16-x) (x=7, 8, 9, 10, 12, 13, 14, 15) solid solution alloys with tetragonal structure were investigated by means of first-principles calculations within the framework of density functional theory. The results of enthalpies of formation and cohesive energy show that the stability of the alloys increases with the decrease of the content In element. The electronic structure was further investigated to understand the underlying mechanism of the structural stability of the SnxIn(16-x) alloys. SnxIn(16-x) alloys exhibit a mixture characteristic of metallic and covalent bonding. A small quantity of In atoms in SnxIn(16-x) alloys may improve significantly structural stability of alloys.