To improve the electric field distribution inside the intermediate joint of the cross-linked polyethylene (XLPE) insulated high voltage direct current (HVDC) cable, nonlinear silicone rubber composite materials for cable joint stress control body are prepared by adding nano-fillers. Based on the tested conductivity characteristics of the composite materials, an HVDC cable joint simulation model is established to calculate the electric field distribution inside the joint. The results indicate that the conductivities of the unmodified silicone rubber under different electric field strength are all smaller than conventional HVDC cable XLPE insulation at 70℃. So the maximum field strength in the cable joint is located in the silicone rubber reinforced insulation and is much larger than the average electric field strength of the cable insulation. When silicone rubber with suitable non-linear conductivity characteristic is used as the reinforced insulation, its conductivity obviously exceeds the conductivity of cable XLPE insulation after the electric field strength exceeds a certain value, thus ensured the maximum field strength is always located in the cable XLPE insulation and close to the average electric field strength.