In order to investigate the effect of ultrasonic treatment on the quality of watermelon juice, the juice was treated with 100 W, 200 W and 300 W ultrasonic waves for 10 min, 20 min and 30 min, respectively. The quality of watermelon juice after ultrasonic treatment was studied. The results showed that the power and time of ultrasonic treatment had significant effects on the quality of watermelon juice, the activity of PPO and POD in watermelon juice gradually decreased with the increase of ultrasonic. When watermelon juice was treated with 300 W ultrasonic power for 30 min, the activities of PPO and POD were reduced by 55% and 40%, respectively. Sonication did not change the acidity of watermelon juice; however, the conductivity of watermelon juice increased with the increase of the intensity of ultrasonic effect. ΔE of watermelon juice after ultrasonic treatment as well as the control group were all lower than 0.8 for watermelon, compared with the heat treatment group, ultrasonic watermelon juice retained the original color better. The viscosity of watermelon juice increased significantly when the ultrasonic treatment time is longer than 10 min, and watermelon juice viscosity nearly doubled after 200 W ultrasonic treatment for 30 min. Compared with the control group, ultrasonic treatment of watermelon juice L-ascorbic acid content decreased slightly, the value of reduction is only 2.7%-23.98% of heat treatment, the total phenolic content was not obvious. Ultrasound treatment retained the nutritional and commercial value of watermelon juice.