Objective To investigate the material basis for the in vivo effect of the effective constituents of Taohong Siwu Decoction. Methods The chromatographic information and information on fragment ions provided by liquid chromatography technique coupled with tandem mass spectrometry were used for the analysis and identification of the constituents (into blood) of Taohong Siwu Decoction given by gavage in rats. Results Based on the analysis of retention time and fragment ions, a total of six constituents (into blood) of Taohong Siwu Decoction were identified, i.e., catalpol, ligustilide, ferulic acid, paeoniflorin, albiflorin, and amygdalin, and all of them were original constituents. Such constituents were possibly the effective constituents of Taohong Siwu Decoction with a direct in vivo effect. Conclusion This experiment identifies six effective constituents of Taohong Siwu Decoction which can be absorbed into blood by the gastrointestinal tract after oral administration, which provides a reference for future pharmacokinetic studies of Taohong Siwu Decoction.