Abstract: Experiments of optimization of the key parameters for fast pyrolysis of elm sawdust were conducted in a self manufactured fluidized bed biomass fast pyrolysis reactor according to orthogonal experiment design, and the composition of bio-oil produced was analyzed with GC-MS. The results show that the optimal condition for bio-oil yield are as follows: pyrolysis temperature 500℃, vapors residence time 0.8 s, particle size 0.180 mm. The maximum bio-oil yield ratio was 46.3 wt%. Pyrolysis temperature and vapors residence time had an obvious effect on bio-oil yield ratio, while their interaction and particle size had unnoticeable effect on it. Analysis with GC-MS showed that bio-oil was the mixture of complex organic compounds with the extensive existence of oxygen. The research has provided a scientific reference for the development of biomass fast pyrolysis technology.