The present invention provides an effective component of rabdosia, which mainly comprises compound A, Coetsoidin F and compound B, and Coetsoidin C; wherein, the content of the compound A is between 70 to 90 percent, and that of the compound B ranges from 5 to 20 percent. The medicinal materials are heated, abstracted, condensed, separated by silicagel column, eluted, condensed and dried with eluent. Then the medicinal materials are separated by a liquid chromatography; subsequently, the solution is collected, and the active component is obtained after the solution is condensed and dried. Therabdosia provided by the present invention can be applied to the preparation of tumour cure and prevention medicine. The method of the present invention is reasonable. The effective ingredient can bequickly and accurately obtained. The quality of the medicine can be easily controlled in production.