Analytical Py-GC/MS(pyrolysis-gas chromatography/mass spectrometry) instrument was used for two-step fast pyrolysis of bagasse, to investigate the product distribution from the first-step fast pyrolysis of bagasse, as well as the effects of the first-step pyrolysis temperatures on the product distribution of the second-step fast pyrolysis process. The results indicated that the first-step fast pyrolysis of bagasse with low-temperature would obtain abundant 4-vinyl phenol (4-VP). The highest 4-VP selectivity was obtained at 250℃ with the 4-VP peak area percentage as high as 48.11%, and the maximal 4-VP yield was obtained at 300℃. The first-step pyrolysis temperature affected the second-step pyrolytic products significantly. As the increasing of the first-step pyrolysis temperature, the content of the levoglucosan (LG) in the second-step pyrolytic products increased remarkably, while the contents of most other products decreased significantly. According to the product composition, the bio-oil obtained from the second-step fast pyrolysis of the solid residues from the first-step fast pyrolysis at 300℃, had better fuel properties than those of the bio-oil obtained from direct fast pyrolysis of bagasse at 500℃. Therefore, the two-step bagasse fast pyrolysis technique was determined, i.e., the first-step fast pyrolysis at 300℃ to produce 4-VP and second-step fast pyrolysis at 500℃ to produce high-grade bio-oil.