Fast pyrolysis is seemed to be an important approach to produce the energy from biomass. Bio-energy offers a clean, renewable source of energy. Its impressive potential makes this technology develop fast. Mobile fast pyrolysis apparatus works as a mobile plant. It could convert the biomass into bio-oil with high quality which will be used to produce other products. The mobile apparatus is designed to have the mobility in order to collect the biomass dispersed in the fields. In this way, the cost of raw materials transportation will be largely reduced. The reactor which is the key component of this apparatus is designed. This new type of reactor is a combination of combustion chamber and reaction space. An annular reacting area is provided by the special structure of the reactor. This construction makes the reactor small enough to seize the space need by the whole equipment. The software of Fluent 6.2 is used for the digital simulation of fluidization condition in the traditional reactor and the new one. The results show that the fluidization effects of these two reactors are almost same under the cold condition. The new type of reactor is proved that is adequate to the job. Comparing with the traditional reactor, the new one has the characteristics of high thermal efficiency, compact, easy operation, etc, which make it well suite to the mobile operation.