Abstract: A series of acrylatestyreneacrylonitrile（ASA）coreshell structure copolymers were synthesized in a two staged emulsion polymerization with PBA particles as core phase and styreneacrylonitrile(St-AN) comonomer as shell phase. Effects of ASA contents, w(PBA) and w(AN) on plasticizing and impact properties of rigid PVC were investigated. Results indicate that the melting time of PVC is becoming shorter, while the counter balance torque and maximum torque increase with the increasing of the ASA content. In addition, the brittle and ductile features for blends in brittleductile transition regions are proved by SEM observation.The melting time gets shorter, while there is a small upward trend for the torque and the notched impact strength of the PVC blends with the increasing of w(PBA) in ASA. With the increasing of w(AN) in the shell phase of ASA, the melting time does not change sharply, while the torque increases gradually. And the notched impact strength decreases when w(AN) reaches 0.40.