The phase composition and structure play an important role in the high-temperature oxidation resistance of the bonding layer alloy. Furthermore， the high-temperature oxidation resistance of the alloy strongly affects the working life of the thermal barrier coating prepared. In this paper， the effects of different Hf contents on the phase composition， structure， and isothermal oxidation process at 1150 ℃ are investigated by Thermo-Calc， X ray diffraction， and field emission scanning electron microscopy. The results of theoretical calculations and microstructure observations indicate that the phase composition of NiCoCrAlY alloy containing 0.5% （mass fraction， the same below） and 1%Hf are mainly composed of the γ'-Ni₃Al phase and the β-NiAl phase. As the Hf content increases from 0.5% to 1%， the liquidus temperature of the alloys decreases from 1422 ℃ to 1418 ℃， the solidus temperature decreases from 1297 ℃ to 1287 ℃， and the solidification temperature range increases. Furthermore， the precipitation temperature of the α-Cr phase increases from 860 ℃ to 880 ℃ with increasing Hf content. The β-NiAl phase content of the bonding alloy with 0.5%Hf in the temperature range of 1000-1250 ℃ is higher than that of the alloy with 1.0%Hf. The isothermal oxidation analysis for 200 h shows that the mass gain versus oxidation time curves follow the typical parabolic oxidation kinetics. As the Hf content increases from 0.5% to 1.0% in alloys， the average oxidation rate increases from （0.15±0.008） g·m^-2·h^-1 to （0.32±0.006） g·m^-2·h^-1， and the parabolic oxidation rate constant k _p increases from 4.163 g²∙m^-4∙h^-1 to 9.337 g²∙m^-4∙h^-1. According to the phase analysis and morphology observation of the oxide layer， it is found that the oxide layer is mainly a dense Al₂O₃ layer； the white contrast HfO₂ phase is also distributed in the oxide film. With the increase of Hf content， the distribution of the HfO₂ phase in the oxide layer changes from discontinuity to continuousness， and the number and area of HfO₂ particles increase. Meanwhile， the internal oxidation degree is aggravated and the thickness of the lean Al layer is improved.