Abstract: Ultrasound-assisted ethanol extraction method was used in the extraction technology of red pigment from red skin red skin (RP) and white meat red skin (WP) pitaya peel. The red pigment extraction process was optimized by single factor and orthogonal test, and the two kinds of red pigment purified substances were identified. Total reducing power and free radical antioxidant activity were determined and compared. The results showed that the red pigment of pitaya peel was identified as betalains by spectroscopy and HPLC-MS/MS. The optimal extraction conditions for WP were as follows:40% ethanol, ratio of material to liquid 1:40 (g/mL), ultrasonic time 25 min, ultrasonic temperature 40℃, and the maximum yield of pigment was 0.856%. The optimal extraction conditions for RP were as follows:40% ethanol, ratio of material to liquid 1:30 (g/mL), ultrasonic time 15 min, ultrasonic temperature 30℃, and the maximum yield of pigment was 0.915%. The yield of purified product obtained by RP in its purification process was 1.232 times that of WP. Within a certain concentration range, the betalains of the two pitaya peel had strong total reducing ability, but slightly lower than V_C, and the IC₅₀ for removing DPPH·free radicals and hydroxyl radicals (·OH) were 1.15 and 0.95 mg/mL respectively. The maximum clearance rates of nitrite (NO₂^-) were 22.90% and 25.10%, 5.95 and 4.57 mg/mL, respectively. The comprehensive antioxidant capacity of betalains of red meat pitaya peel was better than that of white meat red skin.