The oxy-fuel combustion CFB technology as a promising carbon capture technologies needs to study the scale-up process for the commercial diffusion. Numerical simulation would be a rational tool to investigate the gas-solid flow and oxy-fuel combustion process before constructing an expensive and complicated industry-scale plant. A three-dimensional (3D) CFD simulation according to the Eulerian-Lagrangian approach was applied to simulate the hydrodynamics of gas-solid flow and oxy-fuel combustion process in lab-scale, pilot-scale and industry-scale CFB boiler (from 0.1 MW_th to 330 MW_e). Results present the differences of the boiler configuration, the gas-solid flow and the oxy-fuel combustion characteristics between lab-scale, pilot-scale and industry-scale CFB boilers. The cross-section thermal load gradually decreased, while the cross-section area increased with the thermal inputs increased. In the lab-scale and pilot-scale oxy-fuel CFB, the particle velocity field was more uniform than that in the industry-scale CFB. The carbon conversion ratio increased with an increase in the thermal input. The emission of CO, NO and SO₂ in the industry-scale oxy-fuel CFB boilers was lower than those in the lab-scale and pilot-scale. A larger oxy-fuel combustion power plant is beneficial to carbon capture and low pollutant emission. The results would be beneficial to the design and operation of industry-scale oxy-fuel CFB.