The invention provides a method for determining three active components in a medicinal preparation, which comprises the following steps: adding water to dissolve the medicinal preparation, fixing the volume, performing shaking uniformly, performing filtering, detecting the obtained test solution by high performance liquid chromatography under double detection wavelengths, and determining the contents of the three active components in the test solution: catalpol, rehmannioside D and regallily glycoside B. The method for determining the three active components in the medicinal preparation is accurate, reliable, simple, convenient, rapid and good in stability and repeatability, provides a basis for systematic evaluation and quality control of the pharmaceutical preparation, provides a research basis for reasonable development and application of the pharmaceutical preparation, can more comprehensively guarantee the quality of the medicinal preparation, improves the safety and the reliability of the medicine are improved, and has a wide application prospect.