Abstract:The paper studied the extraction amount of chlorogenic acid from off-grade Arctium lappa L．by a single factor test the factors such as methanol extraction agent，concentration of extractant，liquid/material ratio and ultrasonic treatment time were determined.The Central Composite Design and result analysis proved that the optimal extraction condition for three important factors were methanol concentration 50%，solid to liquid ratio 1 ∶100（g/mL），extracting time 30 min respectively.Under this condition the extraction amount of chlorogenic acid from Arctium lappa L．was 3.244 mg/g.