A loop, with baffle, fluidized bed reactor (LBR) is proposed in this work. The reactor is developed to match the redox reaction mechanism of catalytic propylene ammoxidation to acrylonitrile. According to its developmental concept, it is able to be applied not only in acrylonitrile synthesis via propylene ammoxidation but also in most of olefins selective ammoxidation and oxidation reactions. In this paper, the relationship between mass transfer coefficient, catalyst recycle rate and the internal structure, operating conditions are investigated in a phi 300 mm cold model fluidized bed. The mathematical model is built up for the reactor. The computational results for propylene ammoxidation based on this model show reasonable good agreement with the phi 219 mm pilot plant data. The prediction of larger scale plant based on this model has been done, and the phi 2800 mm pilot plant data are listed in this paper. The LBR is capable of increasing more than 2.5% selectivity to acrylonitrile when compared with the commercial type reactor when it is employed in propylene ammoxidation.