A coaxial mixer consisting of an anchor and a Rushton turbine was selected as the research object, whose solid sus-pension characteristics were studied with the help of Computational Fluid Dynamics (CFD) method. Based on the Eulerian-Eulerian method and modified Brucato drag model, the just-suspension speed of impeller was predicted, and the simulation results were in good agreement with the experimental data. The quality of solid suspension under different rotation modes was also compared, and the results showed the coaxial mixer operating under co-rotation mode could get the best performance, and a larger anchor speed was beneficial to solid suspension by enhancing the turbulent intensity at the bottom. Compared with the anchor, the inner Rushton turbine played a dominant role in solid suspension due to its high rotational speed, whereas an extremely high inner impeller speed would make the uniformity of solid distributions become worse. Additionally, the effects of solid phase prop-erties were also investigated, the results revealed that the higher the overall solid volume fraction and the smaller the Shields number, the worse the performance of solid suspension, meanwhile the solid suspension was more sus-ceptible to solid density compared with particle diameter within the same Shields number gradient.