Abstract: A process for preparing cinnamaldehyde from cinnamon oil using vacuum distillation and molecular distillation was investigated. The optimum conditions of the process for obtaining high-purity and high-yield product were determined by analyzing the relative content of cinnamaldehyde with gas chromatography. The condition of vacuum distillation was as follows:pressure 1.333 kPa, temperature of total reflux 60-70℃, temperature of collecting the light component 60-100℃, temperature of collecting the middle component 90-115℃, temperature of collecting crude cinnamaldehyde 110-125℃, reflux ratio 2:1. Under these conditions, the purity and yield of the final product were 98.66% and 84.68%, respectively. The purity and yield reach 99.5% and 85.63% respectively after molecular distillation.