We developed a mathematical model to discuss the performance of chemical looping combustion (CLC) of methane in continuous bubbling fluidized-beds. The model considers the particle population balance, oxidation and reduction rate of particles in fluidized beds. It also considers utilization efficiency of oxygen carrier (OC) particles, residence time of particles in each reactor, and particle size in reaction rate. The model was applied for a bubbling coreannulus fluidized-bed process. The core bed was the fuel reactor (0.08 m-i.d., 2.1 m-height) and the annulus bed was the air reactor (0.089 m-i.d., 0.15 m-o.d., 1.6 m-height). The process employed a type of Ni-based OC particles. The present model agrees reasonably well with the combustion efficiency measured in the process. Simulation was performed to investigate the effects of some variables for the process. The present model revealed that the range of circulation rate of OC particles for achieving complete combustion determined the operating range of the CLC system. The minimum circulation rate of OC particles for complete combustion decreased in the considered operating range as temperature or bed mass increased in the fuel reactor. A large mass of the fuel bed was necessary to obtain complete combustion at low fuel reactor temperature. The fresh feed rate of OC particles for steady state operation increased in complete combustion condition as temperature or static bed height or gas velocity increased.