Abstract: The high voltage cable joint is the hot spot position in the line, which restricts the increase of the line load capacity.To explore with the protection box, as well as the protection box filling the influence of different materials of cable joint conductor temperature, it set up the large current of high voltage cable joint temperature rise experiment platform, the contrast analysis of the cable joint did not install the protection box, equipped with the protection box, box for filling in the box to protect traditional sealant and fill four conditions of the experimental data of high thermal conductive materials.The results showed that compared with the case without protective box, adding protective box will not significantly deteriorate the heat dissipation environment of cable joint.However, after filling the protective box with traditional sealant, the heat dissipation of the cable joint was seriously hindered.Compared with that without the protective box, the temperature of the pressure pipe rised by 8.1 ℃.After filling the protective box with high thermal conductivity material, the temperature of the pressure nozzles decreased significantly.Compared with the case without protective box, the temperature of the conductor only rised by 2 ℃, which greatly enhanced the heat dissipation of the cable joint.