The optimum ultrasound-assisted extraction parameters of Vitamin C from Capsella bursa-pastoris was studied by Response Surface Methodology. The main factors of the extraction were selected by the Confounded Fractional Factorial test. The extraction process was optimized by Box-Behnken test. The results showed that the major influential factors of extraction were: ultrasonic time, ultrasonic temperature and material to solvent ratio. The optimum conditions were as follows: 1% oxalic acid, material to solvent ratio of 1∶10 (g/mL), ultrasonic time of 12 min, ultrasonic temperature of 32 ℃ and ultrasonic power of 100 W. In this condition, the extraction amount of Vitamin C from Capsella bursa-pastoris was (54.88±0.22) mg/100 g.