Method for extracting catalpol from rehmannia stem

The invention relates to a method for extracting catalpol from rehmannia stem, which belongs to the medicine technical field. The method comprises the following steps: 1) rehmannia stem and water are heated for backflow extraction, an extract is performed pressure reduction and concentration to obtain a concentrate A; 2) 95% of ethanol is added in the concentrate A, standing is carried out for overnight, a supernate is performed pressure reduction and concentration to obtain a concentrate B; 3) a concentrate B is led to a XAD-16 macroporous resin column, elution is carried out by water, then elution is carried out by ethanol, an ethanol eluate is collected, the pressure reduction and concentration are carried out to obtain a stiff paste; 4) silica gel is added in the stiff paste, dried and a silica gel column is added, elution is carried out by ethyl acetate/methanol according to ratio of 4:1, a target fraction is collected, the pressure reduction, concentration and drying processes are carried out; 5) recrystallization is carried out on a dried object, the processes of filtering and drying are carried out to obtain the catalpol pure product. Compared with the prior art, the method of the invention has the characteristics of strong industrialization operationality, high extraction efficiency, resource preservation and environmental protection.