A compatilizer PP-g-Vi-PDMS for PP/RTV blends was prepared through a melt extrusion-grafting method. The tentative mechanism of the enhanced compatibility effect was discussed. The interfacial tension of PP/RTV blends was calculated based on contact angle method. The results indicated the grafting reaction between PP and Vi-PDMS, which was demonstrated by both the decreasing melt flow rates with increasing Vi-PDMS contents and the appearing of IR peaks at 1260cm-1、1100~1000cm-1、800cm-1 ascribed to Vi-PDMS′s characteristic IR absorption. The compatilizer significantly decreased the interfacial tension of PP/RTV blends. The compatibility of PP/RTV blends was improved successfully using the compatilizer PP-g-Vi-PDMS.