The viscosity and liquid structure of Cu 100− Sn ( = 10, 20, 30, 40, at.%) melts were investigated. Temperature dependence of viscosity and correlation length all shows an exponential decay function (Arrhenius-type equation), which is similar to our former studied Cu-Ag alloys. The correlation between viscosity and liquid structure had been studied. A simple relation between viscosity and correlation length was found. The ratio of and shows a linear relationship with temperature, which is different from our former studied results in Cu-Ag alloys. Among the four Cu-Sn alloys, Cu 80 Sn 20 and Cu 70 Sn 30 alloys have higher activation energy for viscous flow ( , ), activation energy for structural evolution ( , ), and the slope ( ) of the linear relationship of / with temperature due to the Cu 3 Sn clusters formation.