Abstract: In order to study the effect of antioxidant on the growth of water trees in crosslinked polyethylene (XLPE), antioxidant/metallocene polyethylene-crosslinked polyethylene (MPE-XLPE) blend insulation materials were obtained. A water blade electrode method was used to accelerate water tree aging, and it was found that both antioxidant 300 and 1035 can inhibit the growth of water trees in MPE-XLPE blends. The effect of antioxidant on the microstructure of MPE-XLPE blends was studied by thermal elongation, polarized optical microscopic observation, differential scanning calorimetric (DSC) curve and static contact angle, and the mechanism of improving the water tree resistance of the blends was discussed. The addition of antioxidant can reduce the crosslinking degree and spherulite size of MPE-XLPE blends, increase the crystallinity and slightly enhance the hydrophilic properties. It can reduce the area of amorphous region, and make the convergence of materials more compact, reducing the structural defects as well as the water penetration and water droplet formation. And the water in the materials can be evenly adsorbed on the polar groups of antioxidant in the form of molecules. So, the water was not easy to aggre-gate into water droplets, thereby improving the water tree resistance. In addition, through the measurement of mechanical and dielectric properties, it was found that the addition of antioxidant can reduce the mechanical pro-perties of MPE-XLPE blends, slightly increase the relative permittivity, and dielectric loss at higher frequencies, but they still met the requirements on the performance for water tree retardant XLPE cable insulation materials. The conductivity and dielectric strength of antioxidant/MPE-XLPE blends met the electrical performance requirements of XLPE insulation materials for wires and cables.