Effects of high hydrostatic pressure (100, 200, and 400 MPa) and soaking solution (citric acid, calcium chloride, ascorbic acid, and distilled water) on proximate composition, polyphenols, anthocyanins, β-carotene, and antioxidant activity of white, orange, and purple fleshed sweet potato flour were investigated. Total polyphenol content was increased in sweet potato flour of Jishu 98 (white) at 200 MPa with ascorbic acid and Pushu 32 (orange) at 0.1 MPa with ascorbic acid treatment (0.51 and 0.83 mg gallic acid equivalent/g dry weight, respectively), but was decreased in Xuzishu No. 3 (purple) in both high hydrostatic pressure and soaking solution treatments. Total anthocyanin content was declined in all treated sweet potato flour. Nevertheless, high hydrostatic pressure with citric acid, calcium chloride, and distilled water significantly increased the β-carotene content in Pushu 32. Correlation analysis between total polyphenol content, total anthocyanin content, and antioxidant activity suggested that polyphenols are the most pivotal antioxidant in sweet potato flour. High hydrostatic pressure and soaking solution treated sweet potato flour could be potentially utilized in food with acceptable nutritional values.