Introduction: Shizao decoction (SZD) is a classic Chinese prescription which used in multiple kinds of ascites and edema caused by liver cirrhosis, chronic nephritis, etc. However, considering edema and new application of cancer ascites SZD is worth further investigating. Materials and Methods: In this paper, a powerful ultra-high liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry based on the PeakView tool combined with multivariate data processing approach was employed to clarify the chemical constituents and the ingredients absorbed into blood after oral administration of SZD. Results: As a result, a total of 91 compounds (35 ions in positive mode and 56 ions in negative mode) of SZD in vitro were successfully identified. Besides, 25 constituents absorbed into blood were tentatively characterized. Among the characterized ingredients, flavonoids, prenol lipids, coumarins, and derivatives and benzopyrans were also detected, respectively. Of note, some constituents absorbed into blood played a critical role in cancer therapy. Conclusion: Established method was suitable for the rapid analysis and characterization of SZD constituents, and it provided meaningful chemical information for further pharmacology study of SZD.