Fast pyrolysis is suited for conversion of biomass to liquid fuel in the absence of air/oxygen with char and pyrolysis gas as co-products. Nitrogen is usually used as carrier gas and pyrolysis gases include carrier gas and non-condensable gas. To increase its economic potential of the bio-oil production process, a pyrolysis gas recycling unit was proposed in this study. The pyrolysis gas can be recycled and the fresh carrier gas can be added in this unit. The experiment of biomass fast pyrolysis using the pyrolysis gas recycling unit was carried out in a fluidized bed reactor with the wood sawdust as feedstock. The recycling pyrolysis gas fraction compositions were analyzed and compared with the different operating conditions and its effects on the product yields and the bio-oil properties were also investigated. The results show that the operating condition where new N2 added rate is 12.79v% per hour and the excess pyrolysis gas discharged to balance the system flow rate can obtain the economic and safe operation of bio-oil production.