Abstract: The separation properties of sensitive bio-oil using molecular distillation technology were investigated under different distillation pressures. Crude bio-oil is divided into distillate fraction and residual fraction after the molecular distillation process. The yield of distillate fraction increases obviously with the decline of pressure, which achieves the highest value of 56.50% under 700Pa. Most of water is enriched in the distillate fraction while water in residual fractions is effectively removed; water content in the residual fraction under 700Pa is reduced to 4.20%. The distribution of some typical compounds, including acetic acid, phenol, furfural, levoglucosan, etc, under different distillation pressures was studied and the separation characteristic of these typical compounds was obtained; based on that, a separation factor model was proposed and a quantitative evaluation was made on the enrichment behaviors of 14 compounds in bio-oil.