Abstract: The ceramifiable ethylene propylene diene monomer(EPDM) composites with different fiber contents were prepared by taking EPDM as the matrix, kaolin and talc as the functional fillers, aluminum hydroxide as the flame retardant, and the chopped polyimide(PI) fiber as the reinforcement. The effects of chopped polyimide fibers on the tensile properties, thermal stability and microstructure of ceramifiable PI fiber-Kaolin-Talc-Al(OH)₃/EPDM (PKTA/EPDM)composites were investigated, and the ceramicization mechanism of chopped polyimide fiber reinforced composites was analyzed. The results show that the tensile strength of the composites decreases with the increasing of the content of chopped polyimide fibers. When the chopped PI fibers are less than 10:100 (mass ratio to EPDM), the mechanical properties of the composites are good. The ceramifiable PKTA/EPDM composites can be ceramicized after pyrolysis at 800-1 100℃. The addition of 4:100-8:100 (mass ratio to EPDM) chopped polyimide fibers can effectively keep the shape stability of the composites after pyrolysis at 800-1 100℃, and the bending strength of the ceramic products is between 6-18 MPa. The results of thermal analysis show that the thermal stability of the composites can be improved by adding the chopped polyimide fibers. The results of thermal analysis and SEM analysis indicate that the pyrolysis and carbonization of the chopped PI fibers in the char layer form the structure of fiber-reinforced char layer. The PI fiber reinforced structure contributes to obtaining the well-shaped ceramic products in the pyrolysis of the PKTA/EPDM composites.