Abstract: With the advantages of simpler Structure, smaller disturbance and no self-hurt while discarding sabot, the gas-propelled amor-piercing projectile with discarding sabot (APDS) owns its promissing prospect. This paper has studied the gas-filling and ejecting characteristics between the gas chamber in sabot and the environment. Adynamical model describing the sabot-discarding process has been establihed. Theauthors have also given the slarting condition and the parting criterion of the partingmotion during the sabot-discarding. The motion of the gaspropelled APDS has beencarefully calculated Finally, the effect of the gashole area has been analyzed not onlyon the pressure in the gas chamber near the barrel exit, but also on the sabot-discarding time and distance away from the barrel.