Abstract: Objective: This study aimed to optimize the extraction process of essential oil from Cinnamomum cassia Presl. and reveal its effect on flavor compounds. Methods: The aqueous two-phase extraction of essential oil was optimized by orthogonal design, and the yield of the essential oil from Cinnamomum cassia Presl. was employed as the index to evaluate the outcome. The flavor compounds of cinnamon volatile oil were analyzed by Gas Chromatography-Mass Spectrometry (GC-MS) combined with principal component analysis. Results: The optimal extraction conditions were as follows: The mass fraction of ethanol 25%, the mass fraction of sodium dihydrogen phosphate 34%, the solid-liquid ratio 1:15 g/mL, the extraction time 60 min, and the temperature of extraction 35 ℃. Under these conditions, the yields of cinnamon volatile oil and cinnamaldehyde were 2.82% and 0.037%, which were 1.07 times and 1.31 times higher than those of the conventional steam distillation method. Furthermore, a total of 14 and 15 chemical compounds were identified in the essential oil of Cinnamomum cassia Presl. by two-phase extraction and steam distillation method, respectively. The results demonstrated that most of these compounds were terpenes and aldehydes. Compared with the conventional steam distillation method, the main components of the volatile oil prepared by aqueous two-phase extraction were distinct, and the latter contained more terpene components such as α-pinene (59.93%), cadina-1(10),4-diene (10.20%), α-muurolene (7.35%), cycloalfalfa (2.44%) and yilanene (1.50%). Conclusion: The aqueous two-phase extraction has several advantages of mild conditions, high yield and easy recovery of solvent for the extraction of cinnamon volatile oil. It can be used as an effective method for the extraction and separation of volatile oil from spices.