The combination of a coaxial mixer with dense solid-liquid mixing is a new attempt, and no validated model is available for the simulation of such systems and structures. In this work, different models of turbulence, solid stress, drag force, and turbulent dispersion force, were compared. Results showed that solid-solid interactions could not be neglected at low speed, and compared with the kinetic theory of granular flow and constant solid-phase viscosity models, the frictional-kinetic model was more appropriate, while the effect of frictional stress on the results was limited. The RNG k-epsilon model and Clift model could predict suspension conditions and axial concentrations with higher accuracy, and the inclusion of turbulent dispersion force was also helpful to improve predictions. Additionally, the turbulent dispersion coefficient had a significant impact on the results, and the simulated solid homogeneity was positively associated with the coefficient. Finally, a numerical model with a reasonable accuracy was determined.