A method of detecting oxygen leakage. Firstly, a detection wafer having a substrate and a metallic film with a first color positioned on the substrate is provided. Then, the detection wafer is loaded into a reaction tube from a loading chamber, and subsequently, the detection wafer is unloaded from the reaction tube. Finally, a surface of the detection wafer is observed to obtain a second color of the metallic film, wherein if oxygen leaks into the loading chamber, the second color is different from the first color.