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Zirconium alloys are important structural materials used as nuclear fuel cladding in nuclear reactors. Investigation on the initial oxidation behavior of zirconium alloys in low vacuum environment is helpful to understand the oxidation mechanism of zirconium alloys. Zr-0.75Sn-0.35Fe-0.15Cr(mass fraction, %), Zr-0.75Sn-0.35Fe-0.15Cr-0.15Nb and Zr-1.5Sn-0.35Fe-0.15Cr alloys were made into large-grain samples, and then TEM thin samples were prepared by electrolytic double-spraying. By studying the oxidation of TEM large-grain samples in a vacuum tube furnace with a vacuum of 3 Pa at 280℃ and 290℃, the effect of Sn and Nb on the initial oxidation behavior of zirconium alloys were investigated, and the nucleation and growth of ZrO2 grains on the surface of the alloys was also observed. The results showed that the addition of Nb or the increase of Sn content promoted the nucleation and growth process of ZrO2 grains formed on Zr-0.75Sn-0.35Fe-0.15Cr alloy in low vacuum environment at 280 ℃ and 290 ℃ oxidation. When oxidizing at 280 °C/30 min under low vacuum conditions, the addition of Nb content promoted the increase of ZrO2 grain size, while the increase of Sn content made the ZrO2 grain change from spherical to short rod. With the increase of oxidation temperature (290 °C/30 min), the ZrO2 grains on the surface of the Zr-0.75Sn-0.35Fe-0.15Cr and Zr-1.5Sn-0.35Fe-0.15Cr alloy grew up, while the ZrO2 grains on the Zr-0.75Sn-0.35Fe-0.15Cr-0.15Nb alloy had a faster nucleation rate.