AbstractPolyethylene has excellent electrical insulation, but its low thermal stability and breakdown strength limit its application in the field of high‐voltage (HV) and ultrahigh voltage (UHV) power cables. In this work, we have developed a new organic peroxide, 2,5‐dimethyl‐2,5‐di(tert‐butylperoxy) hexane (Bi25), which can efficiently trigger the crosslinking of polyethylene (Bi25‐XLPE). Bi25‐XLPE does not produce gas byproducts and has a longer scorching time. All performance of Bi25‐XLPE sheets fulfill the standard of the 500 kV power cable insulation due to the void‐free nature, higher crosslinking density and crystallinity. In addition, one 500 kV power cable model was constructed by COMSOL, which confirmed the breakdown strength (up to 61.66 kV/mm) and stability of Bi25‐XLPE.