Abstract: Nowadays the cost of the device for preparing bio-oil is very high with low durability. On the other hand, the reactor usually needs exogenous heating. This results in high energy consumption in preparation of bio-oil clean fuel. On the basis of the existing types of fluidized bed reactor design experience, this paper presented a calculation model for designing fluidized biomass pyrolysis reactor. By using the model, a kind of liner type double heated biomass pyrolysis reactor is designed in this paper. Then the main parameters of the reactor are optimized using VB. The optimal reactor is bed diameter 0.221 m with the height 1.445 m.