In order to study the problem of impact strength and rheological properties of propellant substitutes （Cellulose Acetate， CA） assisted with supercritical carbon dioxide （SC-CO₂）， the in-line slit rheometer， drop hammer impact test machine， SEM were used， and the rheological properties， impact strength and cell morphology of product were characterized in varied experiment conditions. Research results prove that， when process temperature is 50 ℃， solvent ration is 1.2 mL·g^-1， flowability of CA is optimized evidently as injection speed of CO₂ increasing. However， impact strength of extrusion product only account for nearly 53.11% of those products prepared without SC-CO₂（when injected mass fraction of SC-CO₂/CA is 0.173%， screw speed is 10 r·min^-1）； SEM results prove that， quantities of irregular foam structure exist in product prepared with SC-CO₂， foam size are both over 2 μm， some of them even reach at 15-25 μm. Impact strength and product appearance could be modified as screw speed increase， product prepared in 14 r·min^-1 attain higher impact strength （nearly 170.33%） than 6 r·min^-1. During the process of propellant substitutes assisted with supercritical carbon dioxide， rheological properties of CA in barrel could be optimized as injection speed， solvent ratio， process temperature and screw speed increase， however， impact strength of CA could be positively modified as screw speed increase.