The invention relates to a method for extracting bioactive substances, and in particular relates to a method for extracting total flavonoids in dandelion. The method for extracting the total flavonoids in the dandelion comprises the steps of firstly removing flowers and smashing the dandelion, sieving to obtain dandelion powder, mixing the obtained dandelion powder with an ethanol solution, heating for refluxing extraction, filtering to obtain filtrate and filter residue, extracting the filter residue once again to obtain secondarily-extracted filter residue and filtrate, finally carrying out vacuum concentration on the filtrate obtained in two-time filtering till the ethanol concentration is 1-3% to obtain dandelion total flavonoids fluid extract, further, adding liquorice powder in the fluid extract, granulating, drying, finishing after passing inspection and manufacturing into capsules, granules, tablets, pills and the like through the convectional method. The method has the characteristics of low cost, low toxicity and low degree of product structure damaging.