The protective capability of a pack aluminized coating and slurry Al-Si coatings of nickel base superalloy K3, and the distribution and effect of Si in coatings have been studied in the present investigation. Static furnace oxidation tests were performed at 900, 1000, and 1100°C up to 5000 hr, and hot corrosion tests were conducted in the laboratory as well as under a “burner ring.” The results reveal that Al-Si coatings are obviously preferable to Al coatings for the resistances to both oxidation and hot corrosion, especially to hot corrosion. It has been found that the solubility of Si in s-NiAl is very low, and Si mainly exists as secondary phases. When the Si/Al ratio in slurry increases, the amount of Si solved in s-NiAl changes very slightly; however, the content of Si in secondary phases increases obviously. The distribution of Si in the coating is not uniform; that is, it is lower in the external zone and higher in the internal zone. By means of process control or pretreatment, the Si-rich barrier can be formed.