Flavonoids were extracted from Codonopsis pilosula by microwave-assisted extraction and its contents were determined by spectrophotometer. The extraction rate of flavonoids were investigated by single factor experiment included alcohol volume fraction, ratio of material to liquid, extraction temperature, and extraction time. The best conditions for procedure were as follows: extracting time is 15 min, extracting temperature is 85 ℃, the volume fraction of ethanol is 70%,  and material to liquid ratio is 1∶30. Under the optimal conditions, the amount of flavonoids in codonopsis pilosula was 2.87%, RSD=0.878%(n=5), and their recovery is between 99%～102%.