Abstract: This study aimed to explore the correlation between the active components and antioxidant capacities in red dragon fruits. Eight common red dragon fruits were used as materials,the contents of betalanin,total phenolic and flavonoid were measured,the antioxidant capacities were evaluated by total reducing capacity,scavenging DPPH,ABTS,hydroxyl and nitrite free radical abilities,and the correlation between the two had been analyzed. The compositions of betanin were isolated and identified by HPLC and HPLC-MS,and the correlation between the contents of betanin compositions and antioxidant capacities was investigated by PLSR. It was shown that there were differences in the contents of betanin, total phenolic and flavonoid in eight dragon fruit samples,the highest contents of betanin and flavonoid were 76.77 and 9.00 mg/L in "Hainan Jindu No.1",respectively and "Guangxi Dahonglong" had the highest total phenolic content which reached 53.01 mg/L. With the exception of hydroxy free radical scavenging capacity,antioxidant activity of pitaya extractive had a significant positive correlation with betalanin content(r=0.936~0.955). There also was a strong correlation between flavonoid and antioxidant capacity(r=0.717~0.956),but there was no such phenomenon in total phenol. Betalain included betanin,isobetanin,phyllocactin and isophyllocactin identified by HPLC-MS. Betanin was the dominant antioxidant component in betalanin,followed by phyllocactin which intramolecular hydrogen bonds between malonyl group and the ortho-phenolic hydroxyl group might hinder the oxidation of phenolic hydroxyl group.