In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and has high deposition efficiency, was used to deposit CrSi coatings on 316 austenitic stainless steel. This system utilised separate Cr and Si targets, and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series of CrSi coatings with different Si/Cr ratios were produced, and their oxidation behaviour at elevated temperatures was investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the oxidation behaviour at 600 °C, 700 °C and 800 °C was investigated and the optimized coating to protect the stainless steel has been identified. The outcome of the research indicated that a small amount of Si (between 4–7 at.%) in Cr coatings is effective in protecting the austenitic stainless steel against oxidation at high temperatures, while a high Si content (around 10 at.% or more) makes the coating more brittle and prone to cracking or delamination during oxidation at 800 °C.