Abstract: Taking the Litsea cubeba oil the research object, the heavy constituent residue fractionation of Litsea cubeba oil was analyzed by gas chromatography-mass spectrometry system (GC-MS) using vanillin as an internal standard to determined quantity of citral. The experiment explored the effect of distillation temperature, distillation pressure and material flow on citral purity and the yield rate molecular distillation technology by single factor experiment firstly. On the basis, the experiment applied L9 (34) orthogonal test with the comprehensive weight score of citral content and yield rate as the indicators to determine the optimal combination of three factors. The experimental results showed that the optimum conditions was 55℃ distillation temperature, 0.18 k Pa distillation pressure, 15 m L/min material flow with 1L inventory. Under this condition, the purity of citral was up to98% and the yield rate was up to 77.2%. The pilot test verified that this optimum conditions could be applied to industrial production.