The invention discloses a polysiloxane additive for improving the anti-aging performance of EPDM (Ethylene-Propylene-Diene Monomer) rubber and a preparation method thereof. The polysiloxane additive is prepared from the following ingredients in parts by mass: 100 parts of silicon rubber, 0 to 40 parts of ethylene propylene rubber, 10 to 100 parts of white carbon black, 0 to 5 parts of hydroxyl silicone oil, 0 to 10 parts of alkoxy silane coupling agents and 0 to 30 parts of capacity increasing auxiliary agents, wherein the silicon rubber is vinyl-containing polysiloxane with the number-average molecular weight being 10000 to 1000000 and the vinyl mol percentage being 0.05 to 20 percent. The polysiloxane additive has the advantages that the maintaining rate on the high-temperature aging resistance performance on the EPDM can be obviously improved; the mechanical property cannot be excessively damaged; the application value is realized.