Abstract: In this study, a method of ultra-high performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF MS) was used to analyze the in vitro components, blood-absorbed components, intestinal content components, as well as their metabolites of Codonopsis radix-Rehmanniae radix praeparata extract. The aqueous extract of Codonopsis radix-Rehmanniae radix praeparata was prepared by aqueous decoction and freeze-dried, and was administered to Wistar rats by gavage at a dose of 2.7 g/kg/d for 7 consecutive days; serum and colonic contents samples were collected at 0.25, 0.5, 1, and 2 h after the last administration. A Supelco Ascentis Express C18 column (50 mm×3.0 mm, 2.7 µm) was used with 0.1% formic acid aqueous solution and acetonitrile as the mobile phase for gradient elution, and the mass spectrometry data were collected in both positive and negative ion modes of the electrospray ionisation source, respectively. The collected data and the self-composition database were imported into the UNIFI platform, and the manual identification and qualitative analysis of each component were performed by combining the relevant information of each compound in the database. A total of 103 chemical constituents including phenylethanol glycosides, phenylpropanoids, flavonoids, furans, alkaloids, terpenoids, amino acids, sugars, and organic acids, were identified in Codonopsis radix-Rehmanniae radix praeparata extract. The drug-containing serum samples and intestinal contents samples were further analyzed. A total of 28 prototypical blood-absorbed components and 45 intestinal content components were identified. The prototypical blood-absorbed components included 6 terpenoids, 3 violet ketones, 1 phenylethanol glycoside, 1 phenylpropanoid, 1 acetylide and polyacetylide, 1 flavonoid, 1 alkaloid, 3 amino acids, 1 saccharide, 9 organic acids and 1 other compound. The prototypical composition of the intestinal content components consists of 4 cyclic enol ether terpene glycosides, 3 sesquiterpene lactones, 4 phenylethanol glycosides, 2 violet ketones, 1 furan, 1 hexanol glycoside and hexenol glycoside, 2 flavonoids, 1 phenylpropanoid, 1 amino acid, 4 alkaloids, 3 organic acids, 1 saccharide, and 2 other compounds. The metabolites were mainly derived from cyclic enol ether terpene glycosides, sesquiterpene lactones, phenylethanol glycosides, alkaloids and furans. The main metabolic pathways included phase I metabolic reactions such as deglycosylation, methylation, and hydroxylation, as well as phase II metabolic reactions such as glucuronidation and sulfation. The UPLC-Q-TOF MS method enables rapid, efficient and accurate analysis of the chemical constituents, blood-absorbed components and intestinal content components of the Codonopsis radix-Rehmanniae radix praeparata extracts, thereby providing a methodological basis and reference for elucidating the pharmacological materials basis and mechanism of action of Codonopsis radix-Rehmanniae radix praeparata.