The work aims to improve high temperature oxidation resistance of power plant equipment and components in high temperature environment. Ni-based alloy coatings with high Cr content were prepared on steel Q345 by adopting arc spraying. Anti-oxidation behavior and oxidation mechanism of the coatings at 750 ℃ were investigated, and comparative analysis was carried out to oxidation behavior of steel Q345 substrate without coating. Cyclic oxidation weight increase test at 750 ℃ showed that, oxidation kinetic curve of the coated sample presented a parabola style, the curve conformed to the parabolic equation ΔW=2.51t0.22 through nonlinear fitting, while the oxidation kinetic curve of uncoated substrate tended grow linearly. The coated samples before and after oxidation were analyzed with SEM and XRD. Continuous constituent phases including oxides Cr2O3 and NiO as well as NiCr2O4 with spinel structure formed on the surface of coatings at high temperature. These phases were uniformly and densely distributed in the coatings, which could effectively prevent oxygen atoms from invading the substrate and inhibit the continuous oxidation process. The Ni-based alloy coatings with high Cr content prepared on steel Q345 by arc spraying exhibits good oxidation resistance at high temperature, which can greatly improve service temperature and service life of steel Q345 components.