Method for extracting cytisine from thermopsis lanceolata

The invention relates to a method for extracting a cytisine from thermopsis lanceolata. The method comprises the following steps: 1) smashing the seeds of the thermopsis lanceolata and extracting the seeds with a solvent; 2) concentrating an extracting solution so as to obtain a total alkaloid mixture containing the cytisine, diluting the total alkaloid mixture by adding water, regulating a pH value until the mixture is neutral or acidic and extracting impurities with an organic solvent; 3) regulating the pH value of an aqueous phase of the total alkaloid mixture in which the impurities are extracted until the mixture is neutral or acidic, then adding di-tert-butyl dicarbonate and reacting a stirring manner so as to convert the cytisine into a N-tert-butyloxycarbonyl cytisine; 4) extracting the aqueous phase with the organic solvent and concentrating an organic phase so as to obtain the N-tert-butyloxycarbonyl cytisine; and 5) removing tert-butyloxycarbonyl protection from the N-tert-butyloxycarbonyl cytisine by using an acid and neutralizing the acid with an alkali, thereby obtaining the cytisine. The solvent is high in recovery rate, thereby being favorable for environmental friendliness. The extracted cytisine is high in purity.