A comprehensive study on Sn macrosegregation behavior in ternary Al-Sn-Cu alloys was carried out by comparative analysis between gravity casting and squeeze casting samples. The microstructure and Sn distribution of the castings were characterized by metallography, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and a direct reading spectrometer. Results show that there are obvious differences in Sn morphology between gravity casting and squeeze casting alloys. Under squeeze casting condition, the grain size of the casting is smaller and the distribution of β(Sn) is uniform. This effectively reduces the segregation of triangular grain boundary as well as the segregation of Sn. The segregation types of Sn in gravity casting and squeeze casting samples are obviously different. The upper surfaces of gravity casting samples show severe negative segregation, while all the lower surfaces have positive segregation. Compared with gravity casting, squeeze casting solidifies under isostatic pressure. Due to the direct contact between the upper surface of the casting and the mold, the casting solidifies faster under higher undercooling degree and pressure. Consequently, the uniform distribution of Sn reduces the segregation phenomenon on the surface of the casting.