Abstract: In order to investigate the effect of oxygen and temperature on antioxidant of watermelon juice , vacuum with high and low temperature treatment was applied . Under vacuum and non-vacuum thermal treatments, PPO activity of watermelon juice decreased with treatment time and temperature. And the differences of PPO activities of watermelon juice after vacuum and non-vacuum treatments were not significant at the same temperature and treatment time (p>0.05) . At 30℃, lycopene content, DPPH free radical scavenging ratio, and Fe2+ chelate ratio did not change significantly regardless of vacuum or non-vacuum. While the indexes above decreased slightly at 70℃ of vacuum condition, but that decreased greatly at 70℃ of non-vacuum condition. It suggested that oxygen had little effect on PPO activity of watermelon, and lycopene could be protected under vacuum condition.