Based on the technology of biomass powder heated by hot solid heat carrier (ceramic balls), an original down flow tube reactor (DFTR) for bio-oil production from biomass flash pyrolysis was developed. The structural design process of the critical parts was introduced in detail and the experiments were conducted to test the performance of each part of the DFTR, including the solid heat exchanger, the particle feeder, the down flow tube, the particle separator and the quencher. The results indicated that the temperature of the solid heat carrier fluctuated little and its feeding rate could be controlled precisely. The solid heat carrier and biomass char can be separated completely. The hollow-cone type nozzle is very suitable for quenching the pyrolyzed gaseous products which can atomize well as the nozzle diameter is 4.0mm and the fluid flow pressure is 0.2MPa. The pyrolyzed bio-oil yield recovering from agricultural residues reached to 43% as this type nozzle is used to quench the condensable vapor.