The invention discloses a method for preparing high-purity wolfbane B, which comprises the following steps: pulverizing Euphorbia chamaejasma, extracting with ethanol reflux, filtering the extract to obtain a filtrate; concentrating the filtrate, recovering ethanol to obtain a thick paste; Add 5 to 10 times the amount of silica gel to the thick paste, mix well, dry, perform column chromatography with silica gel as the carrier, elute with the eluent and collect the eluent; concentrate the eluent, recover the solvent, and obtain Coarse crystals of chamaejamabolin; dissolve the crude crystals with ethanol, add silica gel to mix, dry, and perform silica gel column chromatography for 2 to 3 times to obtain pure chamaejamacin. The extraction and purification cost of the method of the invention can be reduced by about 20%, and at the same time, the energy consumption can be greatly reduced, and the extraction efficiency of chamaejasme B can be increased to more than 30%. The prepared chamaejamasin B has a purity of more than 99%, and is especially suitable as a standard substance for content determination of chamaemachamata medicinal material and related preparation Jiejieling tablets.