Cortex Cinnamomi (CC), Rougui in Chinese, has long been regarded as a medicinal plant and spice in China. Cinnamomum cassia, also called Chinese Cinnamon, has been wildly cultivated in China and Southeast Asia with a long history for health care and flavoring spice. Previous studies have proved that it is generally safe and has multiple pharmacological activities, such as antidiabetic and antimicrobial effects. The essential oil is one of the main active fractions in C. cassia. Unfortunately, safrole, a toxic compound, was reported in several species, which need to be carefully investigated. Sample preparation is the crucial first step in analysis of TCMs, which impacts nearly all the later assay steps, including unequivocal identification, confirmation and quantification of analytes. However, the sample preparation step is often not well optimized and frequently considered as an end by a large number of analysts. Pressurized liquid extraction (PLE) is an innovative sample preparation technique which combines elevated temperature and high pressure to achieve fast and efficient extraction of the analytes from the (semi-)solid matrices, which is a promising method VII for sample preparation of TCMs. China is the main producing country, which accounts for more than 80% of the world's production. Therefore, chemical analysis is very important for ensuring the safety and clinical efficacy. In present study, a PLE and GC-MS method was developed for simultaneous determination of seven compounds, including the toxic component safrole in C. cassia. The influence of sample preparation, especially the effect of solvent, on the quantification was also investigated in detail. The dissertation consists of three chapters: Chapter 1 reviewed the distribution, pharmacological activites and quality control of CC. In Chapter 2 the effect of sample preparation on the quantification of C. cassia was illustrated. Furthermore, alcohol was found incompatible to sample preparation of aldehydes due to the aldol reaction. In Chapter 3, a GC-MS method was established for simultaneous determination of seven components in C. cassia and successfully applied to quantification of 15 samples collected from different areas of China. The results showed that cinnamaldehyde was the most abundant compound, but safrole was not detected in all samples. Key words: Cinnamomum cassia, Gas chromatography–mass spectrometry, Pressurized liquid extraction, Sample preparation