We describe the effectiveness of the coarse-grain model of the discrete element method (DEM) in solid mixing in a spouted bed. The coarse-grain model was developed originally to simulate large-scale DEM simulations efficiently, where the coarse-grain particle represents a group of original particles. In previous studies, the adequacy of the coarse-grain model was proven in a pneumatic conveying system and bubbling fluidized beds through verification and validation tests. Namely, In this study, the coarse-grain model is applied to solid mixing in a spouted bed. Agreement of the mixing state is shown between an original particle system and coarse grain model systems. Subsequently, correlation between solid mixing and macroscopic behavior of the solid particles is examined in the present study. The macroscopic properties such as solid-particle spatial distribution, pressure drop and velocity distribution of the solid phase are confirmed to correspond quantitatively in the coarse-grain model and an original particle system. Finally, the calculation efficiency of the coarse-grain model is evaluated. Consequently, the coarse-grain model is shown to be able to efficiently investigate the solid mixing in a spouted bed.