In order to solve the problem of high viscosity of high solid content propellants, supercritical carbon dioxide (SC-CO₂) has been used as a plasticizer to improve its rheological behavior. The in-line viscosity of the CA/CaCO₃ solution was measured by a slit die rheometer during the extrusion process assisted with SC-CO₂, and the Power law was used to describe the rheological behavior of CA/CaCO₃ and CA/CaCO₃/SC-CO₂ solutions. Polyflow was utilized to model the dispersive mixing properties of the CA/CaCO₃/SC-CO₂ solutions. Results show that with the presence of SC-CO₂, the viscosity and pressure of the CA/CaCO₃ solution decreases significantly.And the viscosity coefficient of the CA/CaCO₃ solution at 50℃ decreases by 26.00%, while its non-Newtonian index increases by approximately 16.67%. As the extrusion temperature increases, the viscosity of the CA/CaCO₃/SC-CO₂ solution decreases, and its shear viscosity is less sensitive to temperature at higher shear rate. According to this simulation results, when the CA/CaCO₃/SC-CO₂ solution is subjected to the maximum shear stress, the maximum probability density increases by 20.63% at 50 ℃, which confirms that SC-CO₂ improves the dispersion mixing properties of the CA/CaCO₃ solution.