Abstract: The constant wall flux boundary condition in computational fluid dynamics coupled with the discrete element method (CFD-DEM) remains unresolved and there’s no well-acknowledged method at present. A numerical approach to deal with constant wall flux boundary condition in a fluidized bed by CFD-DEM is proposed in the present work, which allows the particle-wall heat flux, fluid-wall heat flux, and wall temperature to vary with space and time. The influences of the both fluid phase and the solid phase on wall temperature are taken into consideration. The present model is compared with the previous method proposed by Lattanzi et al. Both methods are tested in a gas-solid fluidized bed. The effects of wall heat flux and velocity are considered. The wall-to-bed heat transfer coefficients by the present method agree better with those calculated by empirical correlations than those by Lattanzi’s method, which indicates that the present method is more accurate. The method in the present paper provides a solution to the constant wall flux boundary condition in a fluidized bed by CFD-DEM and can be extended to other multiphase systems.