The invention discloses the use of cardiac glycoside compound 12 beta-hydroxycalotropin in preparing medicines having tumor treating and preventing effects. The cardiac glycoside compound 12 beta-hydroxycalotropin has remarkable anti-tumor activity and is capable of serving as a lead compound for treating tumors; meanwhile, a method for extracting and separating the cardiac glycoside compound 12 beta-hydroxycalotropin provided by the invention is simple, feasible, low in cost, and high in efficiency and yield; the extract is good in quality.