The application of nonlinear conductivity materials is an effective solution to solve the problem of electric field concentration in HVDC cable accessories. In this paper

ethylene-propylene-diene monomer（EPDM） is modified by doping calcium copper titanate（CCTO） nanofiller. When the doping content is lower（2% CCTO）

the composite exhibits better nonlinear conductivity. When the CCTO volume fraction reaches 10%

the nonlinear coefficient will reach 5.40. Simultaneously

the breakdown field strength of the composites with a higher CCTO content is severely degraded. Based on this phenomenon

hexagonal boron nitride（BN） with good insulation and excellent thermal conductivity is employed to dope into EPDM matrix. The breakdown field strength of the co-doped composites is significantly improved

and the characteristic breakdown field strength when φ=10%CCTO/ω=9%BN/EPDM increases to 90.1 kV/mm（φ is volume fraction

ω is mass fraction）

which is 35.9% higher than that of 10%CCTO/EPDM composites（66.3 kV/mm）

simultaneously

the co-doped composites exhibit obvious nonlinear conductivity. In addition

this paper discusses the effect of temperature on the nonlinear conductivity and breakdown characteristics of the composites. The mechanical properties of single-doped and co-doped composites are tested and analyzed. The results show that the doping of two kinds of inorganic fillers can improve the mechanical properties of EPDM

and the tensile strength and tensile elongation of composites increase gradually with the increase of CCTO doping content.