The invention involves a Ligusticum wallichii effective composition, preparation method and its preparation and use. Among the effective components, in the weight percentage, the amount of neocnidilide is 45-55%, the amount of 3-(3,4,5-Trihydroxyphenyl) -2-propenoic acid is 25-35%. The preparation method of Ligusticum wallichii effective composition includes the following steps: disintegrating Ligusticum wallichii crude drugs, adding acetic ester and ethyl alcohol, heating and extracting, thickening the extract into concrete and integrating it with silica gel, separating them with positive phase silica gel column, first using petroleum ether and acetic ester as the mobile phase and getting eluate I, abandoning it, then replacing the chloroform and methanol as the mobile phase and getting eluate II, concentrating and drying the eluate II and getting sample; using preparative HPLC to separating again and getting s, then the sample is product. The chemical component of Ligusticum wallichii effective composition provided in the invention is simple and clear; it is easier to explaining its producing mechanism in pharmacological research and controlling the quality of drugs in production.