Abstract: Hot-rolling, cold-rolling and quenching tests of Zr-Sn-Nb alloy were carried out at 750℃, 780℃, 800℃ and 820℃, respectively. The microstructures of different heat-treated Zr-Sn-Nb alloy and the characteristics of β-Zr and second precipitate particles were studied and analyzed using transmission electron microscope (TEM) and optical microscope (OM). The results showed that N18 contained α+β phases while heating at 780℃ and above, and the higher the heating temperature, the more the β-Zr phases produced. The majority of second phase particles (SPPs) in Zr-Sn-Nb alloy were h.c.p Zr(Fe, Cr)₂ Laves phases with the lattice parameter a=0.502nm, c=0.818nm, which was similar to that of Zr-4 alloy. In addition, there were a few f.c.c. Zr(Fe、Cr)₂ Laves phases with lattice parameter a=0.716nm. The results have been discussed extensively.