Abstract: Abstract: Bio-oil, biomass fast pyrolysis product, has lots of inferior quality. These drawbacks result in a serious impediment for bio-oil's practical applications. Although there are many methods for upgrading bio-oil, there is no effective way to solve the problems existing in bio-oil. The aim of the paper is to find a breakthrough from the bio-oil preparation, which using vacuum pyrolysis method to obtain bio-oil from pine straw at bench scale. The influence of temperatures (400-600℃) and biomass dimensions (150-830 μm) on vacuum pyrolysis were investigated. The reaction temperatures were set at 400, 450, 500, 550 and 600℃. The dimensions of feedstock were 150-180, >180-250, >250-380, >380-830 μm. The optimal temperature was 500℃ and at this temperature the biomass with dimension of >250-380 could yield the highest liquid product (about 52%) and the lowest solid product (about 25%). The gas and liquid products from vacuum pyrolysis biomass in the optimal condition were analyzed by GC, GC-MS, FT-IR. The gas product contains H2, CO, CO2, CH4 and CnHm. At the beginning of the reaction, there were high percentages of CO and CnHm in the gas product. With the proceeding of the reaction, the percentage of CH4 became higher and the percentage of CO2 became lower. The percentage of H2 and CO reached its highest point at 40 min. The pH value of the bio-oil was a little low (2.16). The water content was 46.2%. The viscosity (5.2 mm2/s) was better than that of bio-oil from other pyrolysis methods. Using the area representative compounds content, the GC-MS results indicated that the phenols and ketones were the main compounds in bio-oil, which were 21.98% and 36.55% respectively in the liquid product. The acids contents were 14.27% and the alcohols were 3.08%. The vacuum pyrolysis method, for its simple structure and easily operation, can be a potential way to obtain bio-oil from biomass. Meanwhile, compared with the bio-oil by other pyrolysis methods, the vacuum pyrolysis bio-oil has good flow property and a lot of high valuable compounds. It's good for further upgrading and obtaining chemicals from vacuum pyrolysis bio-oil.