To improve the mechanical properties of metal nanowires, alloying is believed to be an effective pathway by adding solute atoms into the host matrix during the fabrication process. In this project, the alloying effects on the mechanical properties and yield mechanisms of metal nanowires have been studied by atomistic simulations. The chemical complexity influence on the softening phenomenon has also been investigated through different alloy systems. The results reveal that softening effects on yield strength can be widely observed in alloy nanowires. The underlying softening sources have been discussed and two major mechanisms have been found: the alloying-induced reduction in stacking fault energy and the increase in atomic size misfit. The weight of two mechanisms on solid solution softening depends on the variation of stacking fault energy and atomic size misfit degree caused by changing the solute concentration, which provides new perspectives to design novel single crystalline metal nanowires.