Elevated oxygen is regarded as an effective approach to maintaining the quality of fresh plant products. To elucidate the role of elevated oxygen in polyphenol biosynthesis and antioxidant capacity, we evaluated the impact of different concentrations of oxygen on polyphenol metabolism, individual polyphenol contents, and antioxidant levels of strawberries during storage. Elevated oxygen (40%, 60%, and 80%) promoted the accumulation of polyphenols, including tannin, flavone, and anthocyanin. At the end of storage, total polyphenol contents of strawberries treated with 60% and 80% oxygen were 1.11 and 1.13 times higher, respectively, than the control group. In addition, elevated oxygen effectively enhanced DPPH and FRAP, which was consistent with the observed changes in polyphenol contents. Additionally, most genes involved in polyphenol biosynthesis were found to be upregulated during storage, with elevated oxygen resulting in higher expression levels compared to controls. These findings show that presumably, the main reason for the improvement in the commercial and edible quality of strawberries is physical treatments, such as elevated oxygen.