Diffusion aluminized coating can grow protective Al2O3 film with high thermal stability, density and slow growth speed in high temperature environment, which is widely against the high temperature oxidation to increase the life and protect the surface. Slurry aluminizing (SA), packing cementation aluminizing (PCA), and chemical vapor deposition (CVD) are three typical methods for preparing aluminized coating. Different coating structures and compositions can be obtained by different aluminized preparation methods, which may lead to difference in high temperature oxidation properties. To explore this difference, a Ni-based superalloy K403 was subject to diffusional aluminizing by three typical methods, and the oxidation resistance were evaluated. The K403 alloy was cut into long squares of 20 mm×10 mm×2 mm as the base materials and was smoothed by sandpaper and then cleaned. By employing methods of SA, PCA, and CVD respectively at 950 ℃, the diffusional aluminized coatings with about 40-60 μm thickness were prepared. High temperature oxidation tests were performed by the SETSYS evolution thermo-gravimetric analyzer (for in situ recording oxidation curves) in the air at 1 000 ℃ for 50 h. Then the surface and cross-sectional microstructure of the coating were observed with a scanning electron microscope (FEI Nova Nano SEM450). Then the component was analyzed by a energy dispersive X-ray spectroscopy (EDS) of each selected point taken by an energy spectrometer. The phase composition of the coating was analyzed by an X-ray diffractometer (D8ADVANCE-A25). The aluminized coatings available at 950 oC by various methods were all composed of β-NiAl phase. However, the concentration of metals particularly Ti diffused into the coating from K403 was method dependent, with variation of the concentration of incorporated metal from high to low in order as follows:slurry aluminization (SA), pack cementation aluminization (PCA) and CVD aluminization. Oxidation in air at 1 000 ℃ showed that the aluminized coating prepared by PCA had the fastest oxidation rate, the CVD counterpart had the slowest, and the SA one was in the middle. The result was attributed to the difference in the concentration of the incorporated Ti, which could affect the β-NiAl coating‘s oxidation behavior, in particular, the phase transformation of meta-stable θ-Al2O3 to stable α-Al2O3. Different from the aluminized coating prepared by PCA which grew a θ-Al2O3 scale, the CVD counterpart with an appropriate concentration of incorporated Ti directly formed a more compact α-Al2O3 scale during oxidation. The incorporation of too much Ti into the aluminized coating prepared by SA lead to the precipitation of more large-sized Ti-rich phases. Its faster external and internal oxidation caused the coating, although it grew α-Al2O3 scale on major area, to have the oxidation rate slower than the aluminized coating prepared by PCA but faster than the CVD one. The dependence of the various aluminizing methods on the mechanisms for the growth of β-NiAl diffusion coatings and the oxide scales on them is discussed.