Abstract: In order to realize the resource utilization of Ganzhou navel orange peel, the pectin (GOP) was extracted by ultrasonic-microwave synergistic extraction from Ganzhou navel orange peel. Box-behnken experiment was used to optimize the process parameters. The modified pectin (MGOP) was obtained by pH modification of GOP. The changes of physicochemical properties of GOP and MGOP were evaluated. On this basis, the antioxidant activities and their effects on corn starch gelatinization and in vitro digestion were studied. The results showed that the highest yield of GOP (18.25%±0.31%) was observed under optimal condition (microwave power 550 W, microwave time 30 min, pH2.4, liquid-solid ratio 25.00 mL•g^-1. After modification, the esterification degree of pectin decreased from 74.10%±2.73% to 33.27%±2.47%, the content of galacturonic acid increased from 74.65%±1.11% to 88.19%±2.98%, significantly. GOP and MGOP showed good antioxidant activity. After modification, the antioxidant capacity of pectin was enhanced. When the concentration of MGOP was 8 mg/mL, the scavenging rate of DPPH and ABTS free radicals reached 84.35%±0.28% and 87.33±0.43%, respectively. Adding 6% GOP and 6% MGOP could significantly increase SDS to 32.05%±0.65% and 43.83%±0.48%, and RS to 14.61%±1.40% and 19.84%±2.76%, respectively. In addition, the addition of pectin also increased the proportion of small particles in starch paste, inhibited the swelling of starch particles, and thus inhibited the digestion of starch. Compared with GOP, MGOP had more significant effects. The results of this study provided theoretical basis and technical support for the development and utilization of Ganzhou navel orange peel pectin.