Abstract: In order to explore the effect of response surface methodology on the extraction purity of seed pectin, the extraction of pectin from seed water melon by ionic liquid was studied with ultrasonic extraction. The effects of ultrasonic power, ultrasonic time, extraction temperature on the content of galacturonic acid in pectin extract were investigated by response surface design.The optimum conditions were as follows: 1 mol/L 1-butyl-3-methylimidazolium chloride ( BmimCl) as extraction agent, ultrasonic power of 300 W, ultrasonic time of 40 min, extraction temperature of 70 ℃.And the ratio of material to liquid was1∶ 20 ( g/m L) . The theoretical value of galacturonic acid content in extracted pectin was 82.42% and the measured value was82.89%.The actual measured value was in accordance with the theoretical calculation.And this research provide the theoretical basis for comprehensive utilization of seed watermelon resources.